If you are still signed in to SketchUp 2019 or 2020, those would count as additional sign ins. Try opening the older SketchUp and sign out, then sign out and in again on the later SketchUp.
If you do go to the account management page, this will show you how to deauthorize all devices:
After doing that you would then sign out, and sign in again, and it will re-authorize the computer you are using.