There are few options in Epcot.
The only place might stay open past 9pm is the Fish&Chips stand, and but it might have been a mistake with MDE on the night we were there. It looked like it might be open until like 9:30pm. I can't say for sure.
One other option that - I think does stay open is the Creations Gift shop, but they only sell a few prepackaged snacks, like gummies, gluten-free cookies, pretzels, regular cookies, and that sorta thing.
One potential option- if you have transportation - is Miller's Ale House stays open late. (2am?) They offer carry out/pick-up and they are not far from the WDW property line. Our orders were ready by the time we arrived, and we ordered on the way over. There are two Miller's. the one closer to Disney Springs (Vineland Rd) is better than the one that's over on 192. It is basic pub food, nothing too exciting, but not bad for late night. I imagine you could probably also get food delivered from there.
There are also some options over in Flamingo Crossing. One that is about to open looks interesting. It is run by the same restaurant group that runs the Italian eateries in Epcot, but it has not yet opened. Hash a Go Go is open until 11pm . Pieology is open until midnight.
There's also a cluster of places on 192, but most close at 11pm.