A lot of restaurants and bars have reduced hours currently. When we were at Poly in July, the only bar that was open was the pool bar and it closed at 8pm.
Here is the list of what is currently open and you can click hours:
https://disneyworld.disney.go.com/experience-updates/dine/#modifications
Bar Riva is scheduled to close at 10pm, which sounds pretty good considering the limited opening/schedules.