I guess the second part of Infinity War, coming up next year. Filming of that one has long been completed. But I'm not up to speed with the MCU at large, so there might be some other minor movie. EDIT: there is Captain Marvel too, already wrapped; and there are rumours that others might have already been filmed, for projects further down the line.
I wouldn't be surprised to learn that he had already filmed one for Spider-Man: Far From Home, that one has wrapped production. It's a possibility that he may have some canned appearances meant for future movies as well, but I think FFH is the last one where they could have physically brought him onto the set.