I asked LG re Xbox Dolby Vision 4K120 support on its OLEDs. LG said:

"The Dolby Vision feature is currently in testing & LG is working closely with its partners to support functionality (including 4K@120Hz) on its 2021 OLEDs soon. More details about models will be shared soon."

— Vincent Teoh (@Vincent_Teoh) May 14, 2021