There lots of things to do on Sunday. Let me introduce a few of them.
Hang Out
I think best thing to do on sundays is hanging out with your friends. You will have a lot of fun with your friends. Socializing is important in these quarantine days but you should wear a mask and keep the social distance.
Cinema
There are lots of movies that you can select and watch. You can deside which movie you will watch before left the home. I suggest you to watch Interstellar. It is a fantastic Sci-fi movie.
Museums
You can go to museums that you interested in. There is 2 museums in my city. I am sure you also have. You can learn new things and have fun.
Cycling
You can bring your bike and cycle with your friends. You will have good time and be fit. Don't forget to wear a helmet for safety.