iMacs with 1TB Fusion Drive and 32 (28) GB SSD blade - unbearably slow boot times

The answer to my own question was given by a senior Apple engineer on the phone with me, and it is negative - for now.

Having spoken to people at Apple Support (here in Europe) who care and listened carefully at what I was saying in order to help them understand the problem, a Senior Apple engineer took the trouble to inform himself about what was going on with Big Sur and Fusion Drive iMacs, called me back, confirmed that there definitely is a problem that has nothing to do with hardware issues nor with any software that would not behave nicely, but indeed with the combination of Big Sur and Fusion Drives. Those of us who have small SSD blades as part of the Fusion Drive system, will indeed see bootup times of in between 4 to 5 minutes before any app becomes responsive, as described by so many users here and on the Developers forum.

What I am publishing here underneath, is what this Senior Apple engineer told me himself on the phone:

The solution: Wait for an update of Big Sur that will fix the problem. Don't waste time trying to run software that checks if all is OK. Don't waste time re-installing Big Sur. Don't waste time installing Big Sur from scratch (clean install). Nothing that has been tried to fix it in the last four months will fix it. It will have to be fixed from inside Big Sur with an update. Find and read the release notes of every update coming out from now to see if the problem was dealt with.

However: Do know that there is no guarantee that the problem can be fixed!...

This is the Apple response (finally) to our big problem.

I will post this in some other threads that deal with the same problem, as soon as I can.

I don't know if you have the patience to try a 9th time. And neither do I know if you have tried the following procedure:

1. Make one, preferably two backups and/or clones of your Fusion Drive. At least one of them should be done with third-party software (e.g. ChronoSync).
2. Start the iMac in Recovery Mode.
3. Erase the Fusion Drive , completely.
4. Do a "clean" install of Big Sur.
5. Make one account during setup but leave it empty for now.
6. Important: once fully started up (you're on the desktop) allow Big Sur to "work" behind the scenes. Don't touch the computer, don't start anything, just let it be for 30 minutes (minutes, not seconds!)
7. Restart your iMac and normally the boot time will now be something like 30 seconds before reaching login screen. The desktop will appear very quickly after that also.
8. Once more, give Big Sur some time to do its business and don't touch anything for about 20 to 30 minutes
9. Restart, check if the boot time is still OK, and use Migration Assistant to copy over all your apps and data.
10. Restart again, check again if the boot time is reasonable, and once again allow Big Sur to have the iMac to its own. Don't start up anything but wait for 30 minutes to do so.

I know one person who has been able to get a boot time of around 1m30s by following this procedure. I can't try it out myself in the near future because I could loose once again one or two days re-installing Catalina and getting things sorted out the way I want and need on my iMac.

Please take a deep breath and relax. I was not offended by you. I am just tired of reading personal opinions instead of answers to my original post, which asks a very specific question to very specific users.

However, we seem to have misread each other's latests post(s). I had missed the one in which you said you have an iMac featuring a 32 GB SSD blade on the Fusion Drive.

Allow me to explain:

1. You say you were not talking about me. But your comment was [quote] in response to Deep Sky Diver [unquote] and that is me. :-)
2. If you were not talking "about" me or "to" me, who were you talking about or to?
3. Big Sur seems to be starting up in a very reasonable time on iMacs with Fusion Drives featuring a 128 GB SSD blade. However, it seems to take forever on anything smaller than that.
4. As I have clearly stated in my OP, clean installing Big Sur on my system (iMac 2019 5K 1TB Fusion Drive with a 32 GB SSD blade) made it indeed start up in about 30 seconds (from Apple logo to functioning desktop). However, right after doing that, I installed the most basic of Apple apps: Pages, Numbers, Keynote, and iMovie, and immediately the boot time went up to almost two minutes. Further installing Garageband, Adobe Photoshop, and Adobe Lightroom (I have no further apps than those) increased the boot time once again to over 4 minutes. This and other symptoms point to problems that Big Sur seems to have with the size of the SSD part of the Fusion Drive. With that conclusion in hand, I spoke to a Senior Apple Engineer, who confirmed for the first time that this was indeed a problem that he and his colleagues were aware of and were trying to find a solution for. Whether or not they will find one and release it in a future update of Big Sur, I don't know but I still give them the benefit of the doubt.
5. I started this discussion, of course, as you can see in the OP. But I did not ask for "experiences of other users". Instead, I asked if any user of an iMac with the specifications I have just given for the umpteenth time (more specifically a 24 or 32 GB SSD blade in the Fusion Drive), was ever able to make Big Sur start up in an acceptable amount of time after installing the necessary apps (like the ones I mentioned). After almost three months of installing, re-installing, clean installing, checking for login items, login daemons, login agents, incompatible hardware or incompatible software, I and many others with the exact same type of Fusion Drive iMac have drawn a logical conclusion. With my OP I just wanted to do a final check before going to Apple and present them with the evidence.

And again: I am not offended. I just answered right to the point. :-)

I disagree with your last sentence. A more or less normal boot time on Fusion Drive iMacs running Big Sur does not depend on "light loads" at startup. Those of us who still have boot times of 4 to 5 minutes before any app becoming responsive, have no login items and almost no launch daemons and launch agents, except those of Adobe and a printer (Epson in my case). Those do not slow down the startup by minutes. The unacceptably long boot times seem to be due to the volume of apps and data on the Fusion Drive. The more apps and data, the longer the boot time. I've tested that out more than once in the past. A clean install of Big Sur (even already 11.1) made my iMac boot in 20 seconds with the Finder and any other 'default' app of the OS being responsive immediately. Adding a few more Apple apps, such as Numbers, Keynote, Pages, and iMovie, however, increased the boot time to 45-50 seconds... Installing Adobe Photoshop and Lightroom Classic increased the boot time to almost 2 minutes... It is a matter of I/O reads and writes, as Big Sur obviously is too "big" to get itself and all frequently used apps onto the tiny 32 GB SSD blade (of which 4 GB is reserved for swapping, making it in reality a 28 GB SSD blade) during startup. Once the boot process is done, the desktop appears, and all reads and writes are over, which takes 4 to 5 minutes, everything is happy and snappy.

The only thing I haven't done yet, is doing another clean install using 11.4 (or 11.5 probably coming soon), and installing my apps one by one, and each time wait an hour or so for whatever process to do its job.

It's an I/O problem, and since there's no more way to find out how fragmented the HDD part of a Fusion Drive becomes over time, it could also partially be due to fragmentation of the HDD part and how Big Sur handles that (or not...).

Anyway, the more apps and data you have on a Fusion Drive iMac, the slower Big Sur starts up. That's the only element in trying to find the cause of the big problem, that seems to be consistent and persistent.

1. You are not telling the truth. Your software is designed to be used for free, BUT also tries to sell the Power User package. And do me a favour, please: change the horribly ugly app icon. It's about the ugliest one I've ever seen in my 35 years of IT.
2. It is YOU who is not helpful. Please read my OP. If you are not using that kind of system, any reply of yours here is useless. I don't have to post the report here because I have done it several times in other threads. I don't need advice about login items, login daemons, login agents or any kind of software that you think is the cause of the problem. I have more than enough knowledge about computers to know what is installed on my system and what is not. You have not read my OP, you're just trying to defend your product. I have clean installed Big Sur, with the same problem arising as soon as Pages, Keynote, and Numbers got installed: the boot time rose from 20 seconds to 2 minutes immediately. Having subsequently installed iMovie, Adobe Photoshop and Lightroom the boot time became a monstrous 4,5 to 5 minutes. Those are the ONLY apps installed on my system.
3. The cause is NOT a failing HDD. It is in perfect shape, according to Disk Utility and other hardware tools I have at my disposal. It is functioning perfectly well, thank you.
4. You completely miss the point about the car comparison. iMacs are not supposed to be booted or run from external disks. Perhaps another comparison could help: It makes me think of the first PCs, having to boot off a floppy disk... Come on... Ridiculous "solution". Macs are supposed to function as they are, without anything else attached to them to help them boot. Even if you or Apple would give me an external boot disk FOR FREE, I would not accept it.
5. The DIFFERENCE in boot times between Big Sur and Mojave or Catalina, as has been established by me and by several other users now, lies in the fact that Big Sur, together with the most essential Apple apps (Pages, Keynote, Numbers...) DO NOT FIT onto the SSD. The OS loads itself from the HDD onto the SSD, with every restart. The 24 or 32 GB SSD blade is too small for Big Sur. THAT is the cause. Unless you can prove me wrong - with logic, not with assumptions about the health of my HDD.