Cannot retrieve from pre-Catalina backups

The idea which I am hoping will still work is to use recovery and the Time Machine backup to go before the installation of Catalina. You can only do this from recovery. So choose a date and restore the entire backup to your External drive. Or even your internal drive if you so wish as long as you have tested the external drive with your current boot install actually boots properly.

You will need to erase the drive before you start the restore and then leave time machine to restore your previous working install. That means you don't need Mojave OS .. since it will be there in the backup. Once inside Mojave I think you have better chance of downloading it again.

If that does not work.. you certainly still need a restore of your previous OS as you cannot migrate easily from Catalina back to Mojave.

Apple might be able to help you if you ask nicely for a boot USB with Mojave.. There are other sources.. google around. Lots of Apple service centres will happily provide you with a Mojave boot USB for a few dollars if you have one near you.

Be assured plenty of people get themselves into the same boat so there are usually a good few articles on how to download the installer. Terminal commands should still work. The first one has a terminal command which only works in Catalina to download mojave.. give it a try.

eg

https://forums.macrumors.com/threads/where-to-download-macos-mojave.2205013/

https://osxdaily.com/2018/09/29/download-full-macos-mojave-installer/

Some will be out of date.. but don't give up.

Also note the instructions to create your own boot USB installer is important. Once you run the downloaded installer it is deleted. And copying it to another location often seems to break it. So my advice is to create the USB immediately. Put a label on it and tuck it in a draw so you always have it.

I have worked through it with several people here. That is why the warnings are there.

If you run into difficulties do post back with details and screenshots if possible.

Read carefully the second part of this document on using Time Machine from recovery to restore all your files and OS.

https://support.apple.com/en-us/HT203981

And how to erase a disk.

https://support.apple.com/en-us/HT208496

Catalina made dramatic changes.

For now those backups on the TC are vital to your recovery.. so do not continue using it for backups. I encourage people to use the archive option in the TC so they are working from one step removed.. but it will depend on your setup. You can never have too many USB drives as you juggle these things around.

"Disappearing backups" is a common issue reported by countless numbers of users who have "upgraded" to Catalina. We know that Apple has made a number of changes with Catalina as far as Time Machine is concerned, but they have not documented any of them, so it's pretty much a guessing game trying to solve issues.

One of the issues is that Apple completely reformatted your Mac's hard drive when you moved up to Catalina, but the Time Capsule drive is still formatted the "old" way, which cannot be changed. So, Time Machine has to convert new backups from one format to another when backups start with Catalina.

Because your Mac's format was changed with Catalina, the Mac might not be able to read the old backups on the Time Capsule. It seems to work for some users, but others......like me....have had no luck trying to "see" the old backups using Time Machine.

My suggestion would be to power off the Time Capsule and leave it off for awhile......maybe an hour or two......and then power it back up. Now restart your Mac. Wait another hour or so and then see if your "old" backups are now accessible.

Please report on your results.

You can downgrade the computer but you will need to boot the computer to recovery.

Inside recovery you can open the Assistant and use the backup to go back to a date prior to your Catalina upgrade.

This can be messy. I recommend recovery to a USB drive not directly to your main boot drive. Once you are satisfied you have all the files you need back you can clone the USB drive to the main boot drive.

If you were running Mojave you should be able to download it again.. Apple simply block access to downloading it for a clean install. Note this for the future.. you always should create a USB stick installation drive of your Mac OS assuming you don't want to move rigidly to Apple's drumbeat.

Great work.

And thanks for posting back the details. It helps for the next person to have example of successful restore.

Super Important for any future upgrade.. make sure you have a bootable clone of the current drive before you start.

If you had a clone rather than Time Machine backups this would have been as simple as.