Keyboard incessantly repeats letters

After upgrading to Big Sur, my keyboard began repeating several of the letters I type and despite tweaking the key repeat and delay repeat tools in system preferences, I can't get it to stop unless I turn it off and then it becomes so slow it drives me about as bonkers as the original problem does.

It isn't every key, but only several, L being one of them.

I've cleaned the keyboard and googled myself silly and nothing so far works.

Help, please!