PLO50 AQJ6ds nitty to check river?

somehow see something 9875-ish in his hand - which probably would only happen on plo5, but since you identify him as fish may actually not be too far off ^^ ♦
so i think you have value here and even so he will have some flushes, i'd guess you have enough of them beat aswell (here again based on my initial guess would say he showed up with 8 high flush or even just an idiot end straight).
just all his sizings seem kinda weak.

*edit - sure there is some worse cases but as played i'd assume they are rare enough to try and get the rest of value - i myself would probably find a checkbehind quite often as pot is already nice, but i also notice that this could be a leak that needs fixing on my end.

What keeps me away from betting the river is that the flop is 3way which thins the worst hands out. On the other hand I expect most recplayers donk the river with the Nuts.
So 3rd high flush should be a valuebet in theory ip if I remember right so get it in.

If he shoves the river, I think the decision is a bit more interesting. Here I would find it weird if he had the nut flush. Or even 2nd nut flush, when he checks at SPR 0,5.

Can you remember the last time a recreational called river bet with set/straight even when flush got there? I can remember multiple times, from each day.

He donks flop and bets half a pot on the turn, calling a raise. That looks a lot like a set. Give him a chance to make one more mistake and shove.

Yeah probably got too careful with river check. Though villain had something like KJ85 with no fd so obviously way too light call on turn. Likely my thinking was that it's unlikely villain has nut straight on turn when just calling so weaker straight or set is kind of unlikely calling hand when he would need to be afraid of straight on turn and then flush also complete. But yeah weird things happen