Do you mean desktop version?
No they don’t. Generally it’s better to install fresh copies of your extensions from their sources. Often with a new SU version release, there is a new Ruby version and many extensions need to be updated to work. Some extensions have their own installers and need to get a full install instead of just being copied.
If you didn’t remove SketchUp 2020, it’s still on your computer. Each major version release installs as a separate program. You can go back to SU2020 and look at the extensions you have installed. If you used the Sketchucation Tool to install extensions from there, you can install it and use it to install fresh copies of your extension bundle from SCF.
If users could be forced to keep extensions up to date, having them carry over would be a good thing. As it is, every time there’s a new SU version release, there seems to be a spate of posts with users complaining about load errors because they are trying to use old versions of extensions.