Did you upgrade your Windows from 10 to 11 when all this started to occur?
What is the Make & Model of your PSU you are using in your PC?
Was your PC with your RX6900XT working fine before updated your AMD Graphic driver?
If you can't enter Windows due to it crashing, restart your PC 3 times in a row before entering Windows. It should automatically start Windows Diagnostic Menu. Go to Windows Troubleshoot Menu and click on "Restore Windows" to a date earlier from when you installed the bad AMD driver. See if that fixes your issue.
Can you enter Windows "Safe Mode" if so, download and run DDU (Display Driver Uninstaller) and remove all traces of your AMD Graphic driver and restart. See if it now enters Windows without crashing.
Once you enter Windows again run in a elevated Command Prompt/Powershell the following simple command line to check your Windows OS for corruption:
SFC /scannow
Now try to install a previous AMD driver and see if the crashes continues from here: https://www.amd.com/en/support/downloads/previous-drivers.html/graphics/radeon-rx/radeon-rx-6000-ser...
Note: If the crashes continues try installing your GPU card in another PC and see if the same thing occurs. If it does than it is an hardware issue with your GPU card.
also check in BIOS to make sure your GPU card is being properly recognized.
