@catmama - I have only seen this issue when someone used cloning software.
Sadly out of the millions of systems Apple has sold over the years that can support Mojave or Catalina I would say less than a dozen have faced this issue. So its not pervasive!
But I don't know in your case where the corruption is... Is it buried in your backup so when you restored you bought it over from your old systems.
The only way to real fix this is to fully nuke your systems drive. The problem is the newer MacBook Pro’s can’t be easily wiped without making it hard to recover the OS.
So you’ll need to take your system to an Apple Store and just tell them you have some very sensitive data on it and you need to make sure its fully wiped down. Let them have the fun of doing it. As far as your OS and apps. You’ll want to stick with Mojave if you are using older applications as Catalina does not support 32bit apps of extensions. I encountered major issues with my photo editing as I have 3rd party tools which are 32bit and didn’t realize so it made one big mess on my Mac Pro. It took me a week to rebuild my system back.
I would stick with Mojave and you’ll want to go back to your application sources to get fresh copies. As far as your data I really recommend you use a second (or more) drives to host it and only carry what you are actively working on.