I played forum mafia, it's a good mental gymnastics.
Learn a foreign language.
Books and music are helpful things. Listen to music you never had time to search for.
Find soemthing to do with your family, like take a sponge ball and play inside with it, is silly but makes everyone laugh.
Board games, cards, are nice as well.
You can make fitness at home with a routine inspired from youtube.
Find a new hobby in drawing or painting. If a normal canvas is boring, your face can become a make up experiment place.
Write your thoughts, create with words.
Grow some plants indoor.
Construct a maquette of something you like with what you have in your home or can order from Internet. Take clay and make a pot, remake ancient techniques of pottery.
Cook meals for you family or youself, play with ingredients.
Try to have fun in everything.