Late stage of $33 mini Saturday KO, V was probably a reg but I didn't catch particular reads.
Starting from the river, I don't see him bluffing here on this SPR, but does it really make sense for him to play a jack like that (77 checks river)? Would you fold on the turn?

I'd probably click back or shove flop depending on opponent. Make villain commit with his PPs and 7x, which I think is a majority of this range. Sometimes he has Jx, and you gotta go broke.

Weird line, but I think he has a J pretty often here. I can't see what else he might be doing it with. Maybe a 7Ts, 9Ts. Either way river is a fold, unless you had a history of him running three barrel bluffs

Agree with persian on this one!

Surely most 88+ shove Pre with 19bb from BB.. I don't know how often villains go bust on bottom pair when there are much better spots to do so and our range has quite a lot of JX hands in it, especially after flatting the flop don't and turn c-bet.

Stats on villain and reads are really important in a spot like this one.

Readless, on the flop, I like just calling. I get that we might lose value from 7x if we don't raise the flop, but my reasoning is that if villain doesn't have a jack, he is like 10% to draw out on us and if he jas a jack, we are losing 90% of the time. So to me it is a way ahead / way behind situation where I'm just happy that a bet is already in there, but would like to play smallball. (discounting 77 which can be counted in the "I've got a Jack" situations here)
On the river, all jacks that were in our range preflop are still in there (well, for most players), so putting villain on worse than a full house is bold. Some villains would continue with their full range here, but that's where the reads on tendencies are important.
In a vacuum, I would have played it exactly the same.