active player punishes your flop cbet sizing

Well if you think he's "punishing" you then just call, allow him to bluff the turn, and jam it in. In theory he should never be raising this flop that you're behind to unless he has AA maybe.

since I havent seen his hand I dont know of course if he's really been doing that, but I thought it's a possibility and if Im right that some fraction of the population would somehow attack my sizing in above spot (?)

then maybe preventive measures can be taken by sizing up or so [as long as one doesn't have a concrete read on villain]?

Probably just a population play if you're readless - not sure if people at these stakes will bluff raise boards like this, but certainly at higher stakes you would see more of this. I think your sizing is fine on a texture like this - he gets a great price to bluff raise you, and really there's no value hands he could have here that should raise this flop. On the flip side this is a great texture to bluff raise if you're the caller and miss - there's like 200k in the middle now so to raise to 100k with pure air you don't have to win it that often to make money.

I guess his strong holdings dont need to protect, and would want to pick off more from my barelling bluffs and value before announcing themselves by a raise on turn or river? Doesnt this mean [assuming he's some legit reg] by 100% that he's been bluffing (with some backdoors)?

If we barrel some holding, then a raise from him on the river will surely mainly be strong,

and a raise on the turn? [any semibluffs?]

He just gave off freaky vibes immediately just look at his avatar. everything about his appearance was he's bluffing.

It looks like you've got less than 20 BB? I'm guessing in GTO-land middle pair with top kicker and a BDFD might be strong enough to stack off here? Like it could be reasonable to reraise small (to allow for raise-fold bluffs) then call it off if he jams.

That being said, I'll tell you how I play it in practice. I'm starting the flop action with a check most of the time. Sure you risk giving a free card but you also get him to stab with a lot of combos you have crushed. If he bets very small I likely check-raise/ get it in. If he bets bigger I call with a plan to call down on most run-outs.

If villain was OOP calling from the BB I would play it the way you did with a small bet. If BB check-raises you small I would call the initial raise but might fold to additional aggression. I find that BB will defend their blind with a check raise bluff often enough on these dry disconnected boards, but they usually have it if they're willing to put all their chips in (there are no draws to speak of, but if they check raise a BDFD they might jam turn when they pick up equity).

All the above is assuming an active "punishing" opponent as described in the first post. Obviously if we get raised by a nit we just fold.