I open old catalogs I see that all my settings have disappeared

Whenever someone says their settings disappeared, my first thought is that we all make mistakes, sometimes without even realizing it. And so that is my first thought here, because LrC does not delete settings on its own. Deleting settings without user input is simply not a function built in the LrC.

Sometimes this happens because the user had imported the photos twice (perhaps without realizing it) into a catalog, and one set of photos had edits and another set of photos did not have edits. Sometimes, this happens because the user had two catalogs and didn't realize it. (Yes, that's right, the user had one catalog with settings and another catalog without settings, without realizing it). Here is a recent example: https://community.adobe.com/t5/lightroom-classic-discussions/all-my-lrc-edits-seem-to-have-disappeared/td-p/15357206

So search your catalog for a 2nd copy of the photo that does have edits. And search your hard disks for other catalog files.