It seems the S20's will revert back to 60 Hz even if set to 120 Hz as other phones do at times.
https://www.sammobile.com/news/galaxy-s20-will-switch-to-60-hz-refresh-rate-in-some-situations/
https://www.sammobile.com/news/galaxy-s20-will-switch-to-60-hz-refresh-rate-in-some-situations/