Bridge Galleries from CS5? Try creating a new gallery and see where it defaults to on save.
I really don't remember exactly where those galleries used to be stored but it would probably have been in Users Library /Application Support /Adobe/ Bridge CS 5 / .... ?
I would suggest that the you should remake those old galleries (which ran on Flash-player) as html galleries.
I use Juicebox Pro to make galleries but there is a light version of Juicebox included as a plug-in in Lightroom and there is also a similar plug-in available for Ps.
The plug-ins are quite limited in their capabilities but they will build basic galleries while the stand-alone Juicebox Pro is a lot more capable — although it is a little tricky to install in Catalina because it has become necessary to run a script before installing the app. itself.