Increase KeyRepeat Speed in MacOS Big Sur
defaults write NSGlobalDomain KeyRepeat -int 1
defaults write NSGlobalDomain InitialKeyRepeat -int 10

And turn off press and hold if you haven't: \
defaults write NSGlobalDomain ApplePressAndHoldEnabled -bool false

I can confirm they work because I am using these settings. Also make sure &quot;slow keys&quot; is disabled in System Preferences &gt; Accessibility &gt; Slow Keys.
Also, although it seems counterintuitive, I checked all my defaults for keyrepeat entries with defaults read | grep -i 'keyrepeat' and found that I had &quot;KeyRepeatEnabled = 0;&quot; in my com.apple.Accessibility defaults.
So maybe setting that to 1 would override the other above defaults and prevent fast key repeat.
To match my setting you can use the command:
defaults write com.apple.Accessibility KeyRepeatEnabled -bool 0

You need to restart your computer for all of these things to take effect! Logging off and on did not change anything for me.