I think I will go with clean installation of Mojava and return to Catalina when I have to , And I don't have a backup.Making 32-bit programs work in Catalina is a pain in the neck and not future-proof. If you want to run that software, then you should run it in macOS Mojave or another operating system (like Windows on Boot Camp).
You can restore a backup from Time Machine if you have one or install macOS Mojave on a new APFS volume. If you tell me which route you would like to go, I can give you further help.
No, I mean clean installation on Macintosh HD and downgrade to Mojava.Yes, the App Store is the only source. Apple has a guide for installation on a separate APFS volume here: https://support.apple.com/HT208891.
No, I mean clean installation on Macintosh HD and downgrade to Mojava.
And is there a way to have my current system preference setting the same when downgrading to Mojave ?