MacOS Big Sur bug - system preferences for key repeat speed keeps getting reset

Boot into Safe Mode according to Start up your Mac in safe mode - Apple Support and see if the problem persists. Reboot normally and check again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

Greetings lorcan458!

From your post we see you are having some trouble with your repeat key speed setting resetting on your Mac. We can certainly see how that would be an issue and are happy to help! Since this issue is occurring with a default macOS feature, we recommend updating to the latest macOS version available for your system: How to update the software on your Mac. If the issue continues you may want to fully reinstall macOS as well: How to reinstall macOS.

Take care!

I'm having this exact problem...Terribly annoying, double spaces and words which seam to constantly have to be respelled. I have the latest MacOs, so the solution offered doesn't fix the issue.