Posted December 31, 2021
If you still have this issue, in a different thread a user reports running as administrator worked:
https://www.gog.com/forum/general_beta_gog_galaxy_2.0/gog_galaxy_cant_update_my_games/post4
https://www.gog.com/forum/general_beta_gog_galaxy_2.0/gog_galaxy_cant_update_my_games/post4