Unless I'm misreading this, I'm like 90 percent sure you should fold pre lol. With 30 bb, this is not a hand you should be flatting in the sb. Being shallow enough at 30bb , this category of hand loses value as it doesn't realize its equity often or benefit from the implied odds it would if you were deeper.

As for your frequencies, I would imagine with a nut and range disadvantage on this board you would optimally check. Although seeing as you're already getting out of line. Perhaps you should lead out for half pot. If villain folds 1/3 of the time, you've got a winning play lol.

It's actually a 100% donk bet according to this GTO trainer. It does make sense if you think about it. It was surprising to me too.

It's about a 47% call preflop with the range used by the trainer. And the SB's calling range is actually a slight favourite on that flop, so that's why it donk bets. Try it yourself and see. My ranges showed equity about 53% vs 47% on that flop.