Using an anvil and enchanted books, you can apply enchantments such as feather falling, respiration, and aqua affinity to any piece of armour, not just the piece they are meant to be on.

This also seems to work for other things, such as sharpness or efficiency on tridents and thorns on shields.

This does not work for exclusive enchantments such as the different protection types

This does not work using the /enchant command, and doesn't seem to work in enchanting tables, only anvils.

(Tested on 2 different computers, and realms, so doesn't seem to be an installation thing)

Also tested on 1.18 1.19, 1.19.4, and 1.20