Kind of a situation normal and super weird 1-2 spot:

V has been very passive preflop, and even earlier streets, in multiple hands. Also maybe has an "okay" range, just limping instead of raising. Have seen him open limp AA x2, JJ and AK all UTG but also a few things like QTs. Possible his range is too wide but he's been running hot.

OTTH:

V limps UTG
2 more limpers
I limp in SB with KxT♠️
BB checks

Flop: A♠️Kx9♠️
checks around

Turn: A♠️Kx9♠️ K♠️
I bet $4 into 10
BB folds
V calls
everyone else folds

Could maybe go bigger here, esp. as so many 1-2 players don't care about the size of the pot relative to bets in limped pots. Didn't really want to get raised though.

River: A♠️Kx9♠️K♠️ Tx
I bet $10
V snap raises to $20
H ???

I tanked here, wasn't sure if I should raise to 50-60 or just call ... the biggest problem with the raise is if he then raises again I'm not sure what to do (I know I should fold, but it would hurt a lot). Was trying to think of what worse hands he plays slow and raises and could only come up with Q♠️x♠️ (maybe just Q♠️J♠️) and K9 ... but he 100% can have AA/AK, which seems like more combos.
Also I never had AA/AK here, and pretty much never 99/TT.

Absolutely raise. Vil has QJ and flushes here a lot. You have the third nuts, and there’s only 6 combos of better hands max. He probably always bets AA/ AK on the flop, so in reality, he should rarely have you beat if ever.

What he said, plus if he can have AA he can also have 99. And if he can have AK he can also probably have K9. This needs to be a raise.

Worry about the 4 bet if he 4 bets. In the meantime raise for value b/c he's got a ton of worse hands he can call with

You have a large full house. Bet the most that he'll call. He might have the nuts. If he does, that's poker. He might jam and raise all in. Then you make the decision.

To have hands better than you, he'd need AA or AK, have seen that flop, checked. then just called your bet of 4.

In terms of the hand ranges and how people play, it's 1-2 against rando players. I swear some don't know how to tie up their shoelaces. I wouldn't expect everything that happens at the table to make sense.

He can have nut flush, K9s, 99, TT. I would raise / fold.

Results (punt, confirmed):

At the time I immediately thought "so I just raise to 60 now" and then I started to second guess myself remembering the AA/AK hands he'd limped which seemed plausible to x/r flop and just call after I bet turn .... I didn't even think of him having 99 until posting, which might have pushed me to raise as I was having a hard time thinking of hands he'd call a 3bet with.

After tanking for over a minute I then thought it'd look even more weird to raise and he might decide to shove QJs/K9 for value so I felt like it was bad but just called and he showed KJ (red) and commented he didn't even notice there was a flush on the board and would have probably called (and confirmed this later by calling against someone else in a similar spot).