Even doing 10,000 - 20,000 steps a day is an important factor in your caloric balance and has positive advantages for your mood. Maybe you can also use your staircase, if you can't leave the house at all.
Do one full song of intuitive dancing a day (obviously this is also really good for your mood)
Daily cold showers, it refreshes your mind and body and keeps you awake and "uncomfortable" in a good way. If you are only just starting try to extent it to a minute. First only your body, then also over your head
Get yourself a (precise) kitchen scale and a calorie/macro tracking app (I personally use MyFitnessPal and recommend it, but there is also FDDB, Lifesum and others). Start tracking your food. Purely at home what you eat is even more under your control than normal. Tracking correctly is a skill (people make mistakes like not tracking small amounts of very energy-dense foods like oil or forgetting to track liquid calories in drinks). Learning it is useful and can inform your intuition about your food choices long term (you will have an idea how many calories a meal roughly have even after you stop tracking, if you pay attention to the numbers). And it can give you the sense of being at least partially in control during these uncertain times.
If this is too demanding, you can also set yourself easier goals like eating 500g+ of fruits and 800g+ of veggies a day