I think that option has been available since way before ios16. The situation for Colemak is still that it’s possible to use an external keyboard with that layout, but there’s no on screen keyboard (unless you use a third party keyboard)
It does take time to learn the Dvorak layout when thumb/swipe typing, but I find the propensity for distance between most letters, except some common cases that prediction nails, to be far preferable to QWERTY.