The moment you installed your 7800XT in BIOS Settings it automatically made your GPU card its Main Display Adapter and your IGPU secondary display adapter unless you specifically set in BIOS to have your IGPU as your Main Display Adapter.
Also as mentioned by @FunkZ the IGPU and GPU card AMD driver are compatible with each other.
So your issue is with the RX7800XT and its AMD Driver and that is what you need to start troubleshooting.
Go to Device Manager and see if you see any type of errors in there. If so which errors are showing?
One way to eliminate the RX7800XT is to disable the GPU Card temporarily in Device Manager and connect your Monitor to your Motherboard to use your IGPU instead. See if you continue to have the same issues.
Make sure you do a Restore Point before you disable the RX7800XT so that you can restore your PC back to the way it was before you did that action.
You can also try some previous RX7800XT drivers to see if it helps fix your problem in case the latest driver has issues from here: https://www.amd.com/en/support/previous-drivers/graphics/amd-radeon-rx-7000-series/amd-radeon-rx-780...
Here is the latest AMD driver for the 7800XT: https://www.amd.com/en/support/graphics/amd-radeon-rx-7000-series/amd-radeon-rx-7800-series/amd-rade...
NOTE: Run DXDIAG.exe and save it to a file. To click on the saved DXDIAG file and go to the last category to see all the files that are having issues with your PC.
Also you can check Windows Event Viewer "ERRORS" to see what other issues you are having with your PC. The errors might be similar to the DXDIAG issues.