when you installed sketchup 2024, it installed a brand new version. meaning you don’t have to reinstall sketchup 2023, it’s still there. check your application folder. you’ll see 2023 and 2024
right now 2024 has not extensions, it’s a clean install. now you can either reinstall manually the extensions you need, or you can copy the old extensions into the new folder and see what needs updating
more about that here
the folders are located in the library, find out where here :