Do you have any other versions of SU installed on that computer?
I think that being logged in on some older version (2019 or 2020) can ‘use up’ one of the licences. So log out of any other version(s) you have signed in on (they don’t have to be running to use a licence, I believe).
If not, then I don’t know enough about the licensing to help further.
In there, select My Products, then for the SketchUp Pro panel click on View Included Applications. In the SketchUp Pro box click on Manage Devices. Then you can deauthorize all.
On the computer you are using you can either close and reopen SketchUp, or sign out and sign in again.