UTG is a straightforward tight passive
Bb is a rec MAWG 2k stack

5/5 1.2K eff

Utg QJ, 4 callers
Flop 9T6 (100)
BB X, I go 60, ugt2 btn and bb call
Turn 3dd (340)
Bb leads 140, I call utg2 calls
River Ax (760)
Bb checks, utg2 uninterested look

Is a stab here spew? What hands does a rec player lead into 3 players OOP (small sizing) and check on this river?

Think you have to stab. You literally never have a worse hand and you don't block busted diamonds.

Not sure why you want to soul read BB here. His preflop range is probably 95% of hands. His flop overcall range can be as wide as any hand that contains a 7, 8, 9, or T, along with JQ and KJ. Guessing at his turn range is impossible. It makes no sense to lead this brick, and the sizing is small enough that he can have anything from clueless Tx to the nuts.

Pretty easy fold on turn.

As played river it's close but I'd just give up. When you call turn a lot of your range is going to be JJ-AA, Tx, and really good diamond draws, so when the river comes A and it checks to you and you bet you're not really repping much imo...

Now that being said I guess we have one of the best bluffing candidates but this is multiway which includes a rec... we don't "need" bluffs here so we should focus exclusively whether we think a x% pot bet will produce folds enough to generate an immediate profit (not that we shouldn't be doing that in other spots but specifically in this spot this should be our primary concern).

As far as the hand goes, I think UTG2 is actually going to have Axdd a lot here. BB can have a wide assortment of hands but we don't really need to bluff here and I don't think a bluff is going to be profitable on this runout with the previous action vs your described opponents.

Doesn't make sense for UTG+2 to have AdXd.

A7/A8dd squarely in UTG2 range.

As is A10.

Ldo AdTd is in his range. As for Ad7d and Ad8d, it would be an insanely loose call for Villain otf with naked gutshot and backdoor flush draw with three to act behind.

Pretty tempting to raise turn. It looks weird but given flop play on this board and the small lead it's really hard to see how either opponent has a hand which can take much heat. There's enough space to raise turn and then bomb river.

If flatting, then yeah you should stab river.

In all honesty, some better reads would make this an easier decision. Is the UTG+2's "uninterested look" appear after the river was dealt? If so, this could be the classic Mike Caro "strong is weak and weak is strong" tell.

Can the BB fold what was a winner on previous street? Does he donk out when he picks up equity?

The ace is a scare card and if you were HU against the BB, it would be an easy stab. Your story would be that you were chasing a FD and had overs or a small pair. You binked the river with an ace which beats the BB's pair of tens. The problem is that the UTG+2 has played if that is his hand. You're never going to get him to fold if he hit is ace on the river.

I don't think you can get through over 50% of the time. If you decide to bet, bet small, maybe $350. You have win less a third of the time to make it profitable. With better reads, you could make a better decision.