I don't eat much to begin with and although being lazy, this prevents me from gaining too much weight. My metabolism slowed down a bit since my teenage years but i am still thin. Don't worry, i don't eat that little to stay skinny, i just can't eat that much

Like i said i'm a lazy guy So i'm skinny but not fit at all. Because i am a video gamer nothing really changed for me other then not going to town for unnecessary reasons.
But if i want to get/stay fit i would probably look on Youtube for a well balanced, not damaging, routine of exercises. We don't need gyms to stay fit. If you don't live in a city you could go out and run some miles as long as you stay far away from other people outside. Although i don't know what the laws in your country say. Here in Germany we can go outside to stay fit (running and walking) near our homes, with enough distance to other people.

I have lost almost 1.5 kgs since it all began. I am doing a lot of cleaning up in my home, getting rid of unnecessary things and removing the clutter. This has led me to walk a lot inside the house. My fitness band has shown me walking around 15-16k steps a day. Plus since activity has reduced, I have reduced my food intake from before and increased my water intake to keep me full. Lesser food and more activity = weight loss.

It can be difficult, but I mostly just find interesting workout/Yoga vids on YouTube and play Just Dance to at least somewhat stay "Active"

I'm always out for a run daily. Tome beeing locked at home isn't an excuse not leaving the house. And I'm practicing social distancing automatically in case a cougar, bear and such crossing my path. Becomes challenging, now with a unexpierenced, fearless dog at my side.

when physical activity become lesser..better to avoid excess intake,use the thread mill for jogging and walking to maintain the fitness

We really did not curtail outdoor activity much, although organised activity disappeared. So football league, I did not do, but that was my only organised activity. The pool was closed for a bit, but is open again now. I am really not into exercise for the sake of exercise anyway, and am slim by default. I prefer just normal activity-type exercise, so that did not change much. Being out of school made it a bit more difficult, but also made it so that I really only was hanging out with 2 particular friends. Now that school is back (part time), it seems a bit easier to get out, but I am finding that I still just do the things which I am in this new habit of doing, hanging out with the same people and doing the same things. This may change in August when we go back to normal school schedule.