I want to follow up with some good feedback that I resolved my crashing problems by making a few adjustments to the settings and I hope that it might help some people here - my theory was to replicate console specifications on my PC and seems to have worked for me touch wood I have a 6900XT GPU and I made the following changes while playing at a 4k (3840x2160 16:9 Widescreen) resolution in Windowed (Fullscreen) mode:
The following critical changes helped:
Set HDR to Off
Set MAX FPS to 60 (even though my monitor is a 55" Alienware that supports 120Hz, reducing it to 60fps made the difference)
Sharpen Image to 6 (this setting can be tested for other values, but I don’t want to change it back in case I break the working settings)
Performance section:
FidelityFX Super Resolution 2 to Off
Other changes which I have done:-
In the Blizzard game window (before you enter game) click on the cog button and then Modify Installation and uninstall High Resolution Texture pack, when you enter the game you can set the Quality to Ultra without any problem (other than the above mentioned changes).
Hope that manages to solve other folks issues facing with GPU issues.
(p.s. I won’t be monitoring replies to this message, as I am busy running nightmare dungeons 
)