Seems you may be the odd one out there. 18.1 has no graphical issue with any 5700/XT with any driver version if you read through the several threads on the steam page. Currently, I'm running drivers 19.10.1 for example. There are others on 19.11, 19.12 and older.
I think this suggests that something else may have gone wrong, such as cached shaders (suppoising this bug is due to a shader problem). Once downgraded to 18.1, could you verify your game files? Also, I hear on forums that a DDU may be required to downgrade from 19.12.2+ (Adrenaline 2020) to older drivers. Could you potentially try that?