I think this can be a fold preflop (to the 3bet; opening is totally reasonable), not that it's a huge mistake to continue, imo. If your suit was higher or if you had two of them or if you had even better connectivity... that'd be a more mandatory call, probably. You just risk being dominated super often.

I think the merits of betting the flop depend a lot on how often villain is folding. I'm in the middle of reconsidering my philosophy of protection bets on the flop in PLO, but it should suffice to say that there aren't a ton of great runouts for you here and you unblock some really high-equity continues for villain.

If villain is going to be folding a lot, that's a reason to end the hand ASAP. If not, that's a reason to keep the pot smaller and not strengthen villain's range by betting.

Because when villain continues, it's going to be a pretty rough ride for you most of the time.

And when villain check/raises, I'm not a huge fan of calling. If you had some more robust equity to draw to, that'd be different. But you've got very few outs to the nuts on this flop: 3 off-suit queens and 2 tens. (Counting 2 nines for the underfull is probably not too optimistic, but it's less of a slam-dunk.)

Luckily, you turned one of those tens and villain played this pretty horribly from what I can tell.

cannot fold this hand to a three bet

This is a mandatory call. Nuttiness is less important in HU pots and even less in lower SPR. It would be a huge mistake to fold to a 3B.

OP pretty much flop the nuts with top2+double gutter at SPR 5ish. I prefer a bet with Kc and is a mandatory bet/call.

devwil your post flop comments are more suitable in SRP where SPR is higher

"Why?

Like, if that's true, I'd really like to learn something."

Think about the implications folding hands like this has on your overall vs 3B frequencies. Now think about what someone who knew those frequencies would do as an exploit. That's a big part of it.