using admin.teams.microsoft.com you can archive a site that you are not the owner of. When attempting to archive and make sharepoint site read-only the operation failed.

I am a teams admin, a sharepoint admin and a global admin and it still failed. Added myself as an owner of the team and it completed successfully.

The error message was "Unable to archive team" very unhelpful. Not sure why a global admin needs to be an owner of the team to archive but if that is required, use a better error message. Or, even do a check and give a warning / grey out the option if it's not possible.