TIL: VIA has the ability to map map most QMK functions with the ANY key mapping (under SPECIAL)
e.g., I’m currently using LT(1,KC_CAPS)
on my CapsLock key so it can function like the Fn
key when held down and the usual CapsLock when tapped.
See Layers | QMK Firmware and Keycodes Overview | QMK Firmware
EDIT: Added example.