This game desperately needs a HDR calibration setting.
Not all HDR is equal, the HDR10 standard is implemented differently among displays.
I have an LG 2017 B7 OLED TV whose game mode preset has a poorly thought out tone mapping system were it treats all HDR content as 4000 nits meaning it is overly tone mapped which causes the darkness in HDR scenes with losing detail (that is not what HDR is meant to look like).
LG have the wrong setting forced in game mode were it should be mapped to 1000 nits instead. You can see this by activating dynamic contrast to low on the HDR Cinema preset, this forces tone mapping to 1000 nits and Sea of Thieves now looks correct (but HDR cinema is way too laggy for use).
Sadly this feature is not preset in game mode and the dynamic contrast setting that is in HDR game mode preset will not change the tone mapping, just making things a little brighter and not restoring detail lost in far too dark scenes.
So you have to calibrate the game to compensate for the bad HDR tone mapping which the game does not provide either.
Please Rare add this feature or consider adding support for Dolby Vision HDR which will display correctly on a DV display as it's designed that way, HDR10 has too many variances.
Thanks.