I would fold river too. Maybe we shouldn't open small pocket from UTG (22-66) but if the table is soft enough why not

You need 31% to call here. Villain needs to be bluffing 1 combo of diamonds for every 2 combos of hearts value for you to make the call. If he is ever block betting with AJo (unlikely with that sizing) then it's an easy call.

I'm not folding this hand when I'm unsure what to do. I don't think it matters much but what would you be calling the river in this situation that plays like this?

bet flop quite often, this hand have close to 0 EV as check down and got to be bluffed (prefered flop to be honest than turn, but turn bluff would be fine as well)
You have heart blocker in your hand, it needs to be called. By his line I expect Ah or QT, and honestly pretty doomed hand for us(hard to imagine bluff in his shoes, he needs to be turn calling some Qd/Td fd and bluff them off, hard to reach nice bluff/value%) but yeah whatever.

I would also cbet the flop.. on this texture we can easily go for a range bet..

River is tricky.. depends on his vpip/pfr.. I think QT is gonna 3bet the turn most of the time, because it's so vulnerable. So I expect only flushes (from his value part) there are AhXh, QhXh, and some lower ones. The problem which I see here is that he is barely value betting worse and I am not sure if he has enough bluffs in this line..
So I think it depends how many flushes does he have in his range (so how wide is he preflop?). Due to your 2x sizing I am a bit sceptical since his calling range is supposed to be wider (Yeah, some guys are calling inelastically vs 2x and 3x) but in general their range is going to be wider. That said, it's much harder to justify calling here.

My reasoning/assumption: with wider range OTR, his value combos are going to increase more than the bluff ones (given the value:bluff ratio)

I agree with folding pre with 33 utg and cbetting on the flop if you open 33 utg on that kind of board.

When you check the flop and bet turn, your range won't have a lot of two heart combos. It's mostly Ax, 33, or two diamonds. Against an unknown, I'm definitely calling 33. Villain could show up with two diamonds or weirdly played two pair.