So if Windows is up to date and all drivers for GPU, Audio and System board have been updated then the next likely culprit is corrupted data or a software conflict of some kind. Especially if the issue was intermittent and then gradually got worse to the 100% you are reporting now.
Let’s reset the in game user options:
Right click Windows Start, Open File Explorer
Navigate to C:\Users'Windows User Name’\Saved Games\Diablo II Resurrected
Once the account is created, shut down the computer, wait 60 seconds, restart, log into the new profile and try the app/client.
If that doesn’t solve the issue, then I recommend submitting a ticket with an msinfo attached for further investigation. (instructions for collecting that msinfo report will be on the form.)
Click your name at the top right of this page, click support, click contact support.