semibluffing on a monotone board in position

First, I recommend removing the outcome of the hand next time or put it in a spoiler.
The BB looks a little bit fishy and I don’t think you can 3-barrel bluff against him and I would check it down after the flop lead and try to hit the flush or straight.

Cheers,
SDK1987

I agree the BB does look very fishy. BB has around 20% equity after the flop and even less after the turn. There maybe an argument for a bigger bet on the flop but I doubt you're getting him off this. When the BB calls a bigger bet on the flop you could maybe look at check/calling or check/folding

Cheers,
Dom

Well I think you can bet OTT here, but choose bigger sizing. After he calls my turn bet and I miss, I'd just check OTR.
Obviously you can only check OTT and take a free card in position, that is ofc a good play too.
The thing is if you bet OTT, you can still make him fold, you build up the pot in case you hit, and it's more likely that he will only check the river if he calls you, so you will be able to easily check behind if you miss. However if you check OTT, you risk less money, but all the advantages that I said above aren't here. He can try to bluff u out of the hand with a stab after u checked the turn (which isn't end of the world since you don't risk much money, so you can easily fold), but the pot is gonna be small if you actually hit OTR, so you will win less money too.
I would say that if you're willing to risk more to win big if u hit, then bet turn, if u don't want to risk, then check.

That one is a tough cookie. I think I'd just check it down after the flop, and hope to hit on the river.

I can see the logic of the flop bet after two checks, but I think I’d check back the turn after villain calls. I’ve read that it’s usually more +EV to do so in position, because we need a lot of fold equity for betting to be better.

Definitely fold preflop and you can easily avoid the problems like this.
But as played check OTF, we haven't enough fold equity, sometimes UTG may slowplay his nuts FD. Then if all the players would also check OTT, I would usually bet T and R as well.

We should fold preflop or 3b as a bluff. Just calling will lead us in more problematic situations and we will be dominated too.

As played, xb turn.