Its cold, but Washington Monument, US Capitol, Botanical Garden limited opening, King Street Waterfront definitely worth a visit during COVID times ( a bit of normalcy). Outdoor drinks ok as long as in non glass cup. The waterfront there is hopping - relatively speaking. You can rent an electric powered bike and tool around the city and points further. Mt. Vernon is also open last time I looked. I'm obviously on the Virginia side and can't speak to Maryland. Also, Tysons Corner Mall and Galleria are open. Also, Lincoln Memorial, Arlington Cemetery, WWII Memorial, Korean and Vietnam, all fairly close together. National Harbor in Maryland

That should fill up a good amount of time, let me know if you want more suggestions. PM me if you want a COVID free tour guide or coffee partner.