The "favorites" is a special runtime that's just "shortcuts" to stuff elsewhere in your runtime collections. The "Favorites" really lives in (where ever you installed your Libraries) / Runtime / Libraries / Collections /

Yeah it's called "Collections" in the file system. If you deleted that whole runtime it would remove the favorites. If you backup your runtimes that folder would be included.

Favorites can get messed up if you rearrange the runtimes. Either by moving folders or installing in a different folder.

I think that's every thing you never wanted to know about Poser's favorites.