Microsoft has started testing Dolby Vision gaming on Xbox Series X/S ahead of a public roll-out. However, Dolby Vision currently gets applied to all HDR games and is limited to 60Hz.
Dolby Vision gaming
In September 2020, Dolby and Microsoft announced that Xbox Series X and Series S will be the first game consoles to support Dolby Vision HDR for gaming, in addition to the base HDR10 format.
Microsoft has now started testing Dolby Vision support for gaming on Xbox Series X and Series S as part of its 'Alpha Ring' that users ("Insiders") can sign up to in order to receive early software builds, as reported by XboxDynasty.de.

Dolby Vision gaming on Xbox Series. Photo: @OzeanSunny via XboxDynasty.de
At this time, Dolby Vision gets applied to all games that support HDR10 (and 'Auto HDR'), meaning that the Xbox system is performing a type of conversion or adaptation – much like Xbox Series X's questionable Dolby Atmos implementation as well as PS5's questionable HDR implementation. In September 2020, the two companies hinted that only select games will support Dolby Vision so it could change in later Xbox software.
Furthermore, and as noted in FlatpanelsHD's review of Xbox Series X, Dolby Vision on Xbox Series X is limited to 60Hz with current TVs. Xbox Series X/S already support Dolby Vision for video.
Microsoft has said that Xbox support for Dolby Vision gaming will launch sometime in 2021.
- Source: User reports, Xbox via XboxDynasty.de