Raise the flop to something like .50. You block spade draws that are not giving up to a raise, and we can check behind on turn IP if we miss. On this board texture I don't expect to get shoved on or 3-bet very often so raising a lot better than flatting. Also disguises our hand if the flush comes. On a super wet/connected board though I'm always flatting IP or OOP here.
As played just flat river. I expect to see a flush/boat here almost always from these type of fishy players. His range is pretty strong for donking out, check-calling a PSB when the flush fills, and donking PSB OTR. When people donk out PSB OTR and have shown strength OTF/OTT, they usually do that in a last attempt to get value and don't want you to check behind.
Not too many worse hands are going to call our shove/raise here. Maybe 8/9/10 high flushes, but even those fold if Villain is somewhat competent. As played, flat river but we probably shouldn't be too happy about it. This line is almost never a bluff.