Catalina: Spotlight can no longer launch many apps
This is a rare situation, but I’ve had great success making a new volume sharing the same APFS container and reinstalling a clean OS in a new volume to validate it’s not your disk that’s failing(failed). It’s not at all unique to Catalina and Catalina works great for spotlight in hundreds of machines we have. We’re seeing fewer spotlight issues compared to older OS in fact.



Back to what you can do - installing a new OS to the same container (to test). I would back up all your important filed before poking anymore, just in case. Once you have that system set up you can let spotlight run on the new OS and convince yourself it’s just that you have corrupt data on the old volume.

Once you know you have a working system, you can run some apps or just run Migration Assistant to bring the files over. If you lack space to have two copies of everything - boot to the old systems and clean / run a Time Machine backup and restore from there (or just erase and install if you already have a backup) knowing things will be fixed.

The commands you list are nice if they work once, but running them several times rarely patches up a system that’s broken in my experience so the sooner you can delete / walk away from the corrupt data / files / filesystem, the better.

If you really need to isolate the failure, I would run mddiagnose and review the files - it’s a ton of work the first 5 to 10 times you try to understand all the diagnostic files - like finding a needle in a haystack, but most failures can be identified from the diagnostic output.