Fretting isn’t the part that requires dexterity. It’s the picking. Picking requires much more fine motor control than fretting.

That’s why right handed people fret with their left hand. It’s the weak hand and fretting requires less dexterity, leaving the dominant hand free to do the hard part.

If you picked up a left handed guitar, you could almost definitely figure out the fretting within a few minutes. But you’d have to seriously relearn how to pick with your left hand, if you were even able to.