So it's very, very hard to see but with some really close-up examination and some macro photos I found some pins on one of the chips on the card appear to be damaged. I am going to guess that this is probably the cause of my issues - see image.
I think this may have progressively become worse, particularly at high temperatures as I began experiencing 'glitchy' screens as time went on and this wasn't an issue at the start. I hope that driver/software didn't contribute to this.
I am giving up and will buy a new card when I have the money
I do still think there are driver / AMD software issues based on my issues as well the responses and solutions here and the weird fan curves and I really sympathise with the frustrations of anyone experiencing the black screens so if it is helpful to someone here is a summary of the solutions for black screen / BSOD that worked for some:
1.) Clean up drivers with AMD Cleaner and/or DDU, also remove windows drivers while in safe mode. Then install the AMD drivers and software (video here https://www.youtube.com/watch?v=Qh2xEUXWeqs ). - didn't really work for me but it's probably the best place to start
2.) Follow the AMD troubleshooting guide here Troubleshooting Common AMD Graphics Driver Installation Problems - didn't make any difference to me but it's good to check your file system etc to eliminate that
3.) Make sure anything that might conflict with the AMD software is uninstalled (eg. MSI Afterburner or ASUS GPU Tweak) - this is defs a well know issue so do this before you do more complicated things
4.) Use 2019 drivers instead of the 2020 ones
5.) Use a HDMI Cable or If You Still Wanna Use Displayport Disable FreeSync then Change Your Monitor Refresh Rate to 120hz From OSD Options.
6.) Every time you start the PC go into Adrenalin Settings / Display and change the Pixel Display from RGB Full to RGB 4:4:4 or any of the others and back to Full RGB
7.) Try this TDR fix Graphics driver stopped responding and has recovered....TDR fix
8.) If you're getting the Driver Verifier Detected Violation error try this FIX: Driver Verifier Detected Violation error in Windows 10
9.) Switch to a higher resolution monitor
10.) Undervolt the card
11.) Swap out the PSU - this seems to have worked for a lot of people and seems unrelated to the power of the PSU or any specific specs they have in common as far as I can tell so no idea why this would work, but it has helped some people