My wife and I went back in November 2019 ... Months before COVID started. Smithsonian museums clustered around the National Mall, so never a bad idea to go there. Don't make the mistake my wife and I did of being at the supreme court and saying "oh the Lincoln Memorial isn't too far, let's just walk down there". There's a reason there's so many metro stations in the National Mall. Natural History, American history, Air and Space (although it was disappointing when we went because most of it was under renovation), and plenty of others.
Spy Museum is really cool, definitely recommend that. I don't know if Capitol Tours are still a thing after January 6, but if they are, that's usually pretty good and depending on the day and time, there might be parts of the tour that aren't there at other times. For instance my wife and I got to see the old Supreme Court room, which does not always happen.
The Holocaust Museum was really good, but obviously not an uplifting thing, but I definitely recommend it. Arlington National Cemetery is good too, just make sure to go slightly before the changing of the guard at the Tomb of the Unknown Soldier.
I forget what it was called, but there was a fancy (and expensive) restaurant we went to one night, but when we were eating a guy that looked like a manager or something stopped by our table and asked us if we were the ones that asked to go up. We said no, but a minute later he comes back and asks if we want to go up to the view of the Capitol higher in the building. It was an incredible view and we got a picture there. It was pretty close to the National Mall.