PLO50 QQ99ss 3bet pot, hero call river?

With these sizings from villain, my guess would be A2.
Your hand doesnt block anything relevant and you have the flushdraw yourself. Dont see any reason to call.

My thinking was that low straights are not necessarily value betting on this board. Especially when board pair as well. We are also deep stacked so I would not bet necessarily that much with sets or two pair on this flop as its very viable spot for villain to check range.

Anyway my hand is indeed too wide theory wise but also felt like its kind of easy to be overbluffing. One of those spots where I just didnt believe villain. But yeah I think good amount of two pairs (2 boat blockers) I would bluff raise. That leave some straights and few better pockets with straight blockers as call. I think we need some sort of draw to call with overpair on turn anyway.

With these sizings from villain, my guess would be A2.

You usually assign villain a range to a given action. I highly doubt it, that he will have specifically only.

I think blocking the flushdraw and having no wheel card at all by ourself is pretty bad. On the other hand his 3bet BB vs SB can be very loose and will include a lot of unpaired overcards, his flop check-back indicates he has no strong hand so his story of or a random is credible. Those hands compose a very minor part of his preflop 3bet compared to the tons of hands he still can have, an overpair still has decent value on blank river runouts for this reason.

With that smallish bet he is not getting enough value out of it just betting those and he is supposed to bluff frequently too (which he might be doing) so against unknown we have to defend here. We should have already lead 2barrel some part of our top-range ott so we are capped and by having no check-raising range in a spot where it is technically possible our check-call frequency goes up. Beside and we won´t have too many other options considering picking hands we can defend (non-nutted straight will be also rare for us to have in this instance and defending that together with the is not enough). We will run into low straights, underfull and trips quite frequently but with the odds this is totally fine to start off our dynamics lol.

PS: I checked solver solutions. Well arriving otr we have check-called a decent amount of overpairs and we´ll have to check-call 50% of those once more whereas check-folding another 50%. It was quite hard to find patterns, which one to assign to each action because having a specific low-card combo as a sidecard was no clear indicator for calling or folding but we know the situation itself is supposed to be marginal. QQ99 in specific would have been a check-fold otr since solver likes to check-fold all of the double-pairs first and where as QQB is an even mix he starts to go up with the check-calls when the sidecard becomes a or lower which makes sense. But since solver also calls to with similar freqs and I personally prefer calling stronger hands when the blocker does not play a role (because solver would not turn that many SDV into bluffs than the average Joe) so check-calling more :Qx:´s but folding some :Tx:´s is something I personally tend to do.

From villains perspective he will have similar requirements when it comes to finding bluffs and check-backs with his range (beside obvious blocker plays) but virtually nobody on PLO50 is will approach towards that correctly (ie. by using randomizer or counting side-cards) so relying on intuition to apply a halfway balanced strategy mix of check-calling and check-folding while being aware how GTO-freqs look like should be sufficient. After more handhistory you might identify villain sifhting towards an unbalanced inclination (usually checking back too much) which would allow us to adjust.

PPS: As river play is more grayish area and both options are a thing I guess it won´t play a big role EV-wise in general what we do unless we are not falling into one extreme like overfolding anything weaker than trips or stubbornly double-calling any overpair. I think the more important street is the turn we have to check-call that (and other overpairs) when having a flushdraw but folding those without (!). From this perspective I think the hand is well-played overall no matter what you were ending up doing otr.