Restoring from a Time Machine back-up - puzzlement!

deggie's reply is correct.

Rather than concern yourself with the reason TM assigned unique names to the restore source, you really ought to start from the beginning. Describe the end result you are seeking.

The reason is important. You erased that Mac's startup disk, and now you want to restore a backup. Restoring a startup disk from a backup erases it first (TM tells you that) so erasing as a separate step wasn't necessary.

Furthermore, restoring the most recent backup recreates the exact same state that existed prior to erasing it. It gets complicated, because if you select "Macintosh HD" (or "HD 1") you are restoring its Local Snapshot. Time Machine tells you that too. That's a fine idea if your goal is to undo something you did subsequent to that backup's creation.

So, what you want to accomplish isn't clear to me.

Although a peculiarity of this site often results in similar or identical answers (often, existing replies don't appear until a new one is posted) unless I have something constructive to add I don't disturb a Discussion in which its OP is already receiving competent assistance. That's just me. I don't intend to impose that practice upon anyone, and in this particular case there's nothing to add to "you select the most recent backup," regardless of its name.

That's why I didn't reply. I'm replying now because you asked... but your question really needs more explanation: Why did you erase the startup disk?

The one thing I've gathered while seeing various posts on this type of problem is two folded:

1. Fact: Catalina splits the hard drive into Mac HD and Mac HD - Data. The first is the system and not writeable - you have no access to it. The second contains everything else and you have read/write permissions. The only place to see this is in Disk Utility and those two should be listed.
2. If there are two of either showing, it appears that it was a botched install and/or the drive was not erased before a "clean" install. Which would mean to use recovery and erase your drive completely and reinstall from Apple (rather than TM). You would have to use other means (setup assistant or drag 'n drop) to get your files moved over.

I've read on these forums that Catalina splits Mac HD into two separate partitions or identifiers. One is just for data and that might be the one with more data showing. It's an oddity but not anything to lose sleep over.

I do understand, and no I don't think you're crazy. Having said that if you suspect malicious interference with your Mac or anything else, you're always better off inquiring here first (or somewhere else, provided you have confidence in the advice you may receive) before heading down some rabbit hole where you're only going to find more bizarre weirdness likely to feed into whatever paranoia may or may not be justified.

The very last thing anyone should ever do is to install some non-Apple "anti-virus" junk, unless of course it's merely for your own entertainment or to satisfy some morbid curiosity.

It's actually not accurate to say that's the very last thing anyone should ever do. Just don't do it, ever. For example I could describe my experience with "Kaspersky" specifically, but an accurate report would require the use of foul language so extreme no respectable website like ASC would permit it.

Does YOUR Time Machine back-up have both HD and HD1?

No, but I have a great number of TM backups and confess I just don't have the time to exhaustively inspect each one.

As I initially surmised, your question is a bit complicated and deserves more attention than I have been able to devote to it. In light of that limitation, here's what I recommend: First, be sure to obtain and use at least one additional, redundant, Time Machine backup device. You can use it in addition to your existing ones and TM will back up to it "in rotation". Satisfy yourself that TM is working properly with it, which might take a week or two of observing its operation. Then, when you are confident enough, take your existing "My Book", erase it using Disk Utility, and return it to Time Machine's rotation.

Unfortunately that will not address your question regarding the presence of "HD" and "HD 1" but there are too many complicating factors for me to provide anything more than a guess as to its appearance. The screenshot you posted is odd and doesn't resemble my TM backups, so all I can say is "that doesn't look right".

There are valid reasons to periodically erase a TM backup device. If nothing else the sheer number of files (well into the millions) just becomes overwhelming. When I realized some of my backups went all the way back to Lion, I erased them and started over. The length of time you want to keep backups is up to you, but in my case if I haven't required to restore something for several months, it's unlikely I ever will. So I erase it.

It does have a fusion drive. Might that be the cause of seeing HD and HD1?

I have a Fusion drive in my Mini and it only has the one drive backed up, not two.

If you open /Volumes, do you have a Macintosh HD and Macintosh HD1?

You would have had to look before erasing and reinstalling.

I’ve only seen this on external drives, but if the drive gets “lost”, the OS might mount it again suffixing with a 1 since there is already a mount pour by that name.

My guess here is that happened with your startup drive (which I really can’t imagine). Time Machine then backed up both mount points.

This is going to be my last comment here because it is delving into two things I do not use: TM (so I do not know how it works) and WD external drives, especially if they were not erased and formatted before use and therefore still have unnecessary WD software on them.

Your DU screenshot shows the two correct entries for your internal, so that is good. I have no idea what is happening on your external.

Hi. When I updated to Catalina I had the same situation.

As far as I can understand, it has to do with Apple's new APFS file structure. While it looks like there are two volumes there, apparently it's really one and cannot be used as separate storage. Shortly after Catalina dropped Adobe advised Photoshop users not to upgrade to Catalina as there are unresolved issues. Functioning Pshop is vital to my work, so using a SuperDuper backup I restored my original content running macOS Mojave BUT I still have the two disks on my desktop.

My start up disk is Macintosh HD, but other contributors to this forum have recommended using Macintosh HD Data as your boot drive. My 2018 iMac is working okay though. I don't know if this helps. Good luck.