To add to this, KMonad can give you these “QMK”-style tap/hold keys on your laptop keyboard too:

https://github.com/kmonad/kmonad

For example, you can put shift keys under your pinky fingers:

  (defsrc a ;)
  (deflayer main (tap-hold-next-release 300 a sft)
                 (tap-hold-next-release 300 ; sft))

It’s implemented as a virtual hardware device so compared to other methods of remapping keys it’s fairly well supported across applications.