My system: 2400g, Vega 64, 850w psu, 16gb ddr4 @3200. Have had nothing but problems with both assassins creed odyssey (constant crashes) and now metro exodus. Metro exodus starts out fine, but seconds into game the gamma drops so low that you cannot see and strange flickering issues occur. Turned maximum power up to 50 on wattman, recently reinstalled Windows 10 and clean install of 19.3.2. Same issues occurring.
First make sure to report the issues to AMD the more complaints they get the more they pay attention and fix issues. Let them know about it here: Online Service Request | AMD
Next you already did what I would have suggested and increased the power limit to it's maximum.
From here I wold suggest some usual culprits that may or may not help.
Try running the game in borderless window.
Try disabling any in game overlays.
Disable all Windows 10 gaming features.
Use your antivirus programs gaming setting if available.
Disable Windows 10 telemetry. o&o shutup is a good app to do this.
Disable fast startup and hibernation.
Set you computer to high performance not balanced if it is still at defaults.
even if those things don't help these trouble games those changes can help overall stability and performance.
Good luck and make sure to keep reporting it to AMD for every driver that does not fix or list these games as known issues.