(chance of winning * amount won) is minimized with MPNK HU in this hand.

iow, you're not trying to protect your hand on the flop.

surprised to see all agreeing with the flop cap - I would have just called the 3bet unless I had the Js+ - so much too learn...

and yes, donk the flop...

I dunno. It depends on UTG's and MP's (and even CO's) ranges and what UTG and MP will fold and under what circumstances and also what aggressive actions UTG, MP, and/or CO will give and under what circumstances when they don't fold. The math would be very complicated even if we had perfect information. And, in fact, there's a lot of information we don't know.

Given the information that we have, I agree with a flop donkbet. I also agree with a donkbet if we're readless. Basically, on this 4-way flop, given the board and our relative position to the PFR, as a default I like a donkbet.

But I did also provide a scenario in which I would probably checkraise instead: If we had a read on CO that said he was going to auto-c-bet the flop, then suddenly much of our reason for donkbetting (to make sure at least one bet goes in) is eliminated, and now by checkraising we can make sure at least two bets go in. It's true that in the process, we will now be facing UTG and MP with two cold (unless one of them donkbets and CO just calls), which increases the chances they'll be folding. They probably won't fold anything decent -- for instance, driving K6o out probably is too much to expect, and I'm not super-optimistic about getting rid of 9c8h either (although I'm not ruling it out). But if MP folds Ks8d after CO c-bets AcJc and I checkraise, then, sure, it depends also on what UTG has, but I think I prefer the outcome of MP folding his air that happens also to be a ~6 outer against my hand for two cold to the outcome of him seeing the turn at ~11:1 in the face of my donkbet and UTG's call or fold (and the uncertainty of what the PFR will do behind MP).

In short, hand protection is not my first thought on the flop, but I'm not going to go way out of my way to avoid it, either. In some cases it will be beneficial.