I'm experiencing this on iOS 15.0 (19A346) on my iPhone XS, too. Same symptoms as original poster: "q" and "1" keys not tappable in Notes or Mail but "123" and "abc" toggle keys are. I have occasionally been able to get the "1" key to work but it only happens once. Can't touch along whole left side of screen for the most part (once in a while it works). Moving the text cursor also seems broken sometimes (loses the touch on the keyboard as soon as it starts, and then it starts typing letters). Keyboard works fine when rotated to landscape (but not when rotated back). Force-reset doesn't work and neither does resetting the keyboard dictionary. Interestingly, swiping right from the left side of the screen in Notes does show the new note change history.