AJ on the SB

Against such a nit calling AJo isn't a good idea. Hard to "outplay" a guy with such a tight range from OOP. 3bet or fold.

Don't wait for a bad turn card or a check back on the turn, just check/raise on the flop.

On the river it's both tough to value and tough to fold. Nevertheless note that opening QTs from UTG while ending up with a 8% UTG open on a 600h sample is pretty hard. Maybe the sample isn't big enough but I'd discount such combos from his preflop range.
Bet/calling KK on the turn would be stupid as hell, so out. Cbetting 99 on the flop would be too, but that's already way more in the area of his possible stupidity, so keeping it in is fine.

All in all I think it's a fold on the river but it feels weird to raise on this turn to fold on this river, proof that the hand isn't meant to be played that way preflop and on the flop.

I did not 3bet pre to avoid a 4bet given his tight range but maybe this is not the way to think of it?
Fold pre is ok too? Isn't it too nitty?
OTF I should raise because despite his 80% cbet stat the board hits him and I can extract value?

Indeed AJo isn't the hand you want to "avoir a 4bet" with, moreover versus a nit. He 4bet, you fold, happy to avoid KK+ as you made him so face up.

Fold pre is ok, there isn't such a thing as being "too nitty" against nit themselves. SB isn't a playable position for cold calling dominated hands is all.

Remember OTF that 80% cbet is easy to have when you are coming from such a nitty preflop range. It's not the 80% of the guy that bets anything anyhow, it's the 80% of the guy that has nearly always something to bet with.
You floped well but as you saw there are lots of hard runouts for you so way better to raise immediatly.

Yes, his 80 cbet is not from bluff cbets mainly due to his tight range.
Now I get the pre-flop call on the SB was bad and was the primary mistake on this hand imo.
I think the flop check-raise has more merit than the check-call, but the last one is acceptable I think.

totally agree with floxy.
you did well to recognize that the river sucks ass, i believe this is usually either a jam or check/fold spot. check/call only works when the guy's bluffing enough, but the guy is tight so he doesn't have many (any?) low missed flushes, which pretty much forces him to turn some Kx hands into bluff and i doubt he does that.
jamming can't be too terrible, but i like check/folding. most of the time the river should go check/check and we win.

Agree about the preflop 3b/fold. Agree with the river fold too.