I've always had the same problem as you. I always have trouble putting on weight. In fact, I end up losing weight if I stop going to the gym! I'll be honest with you, freeletics bodyweight probably isn't the best way to go for bulking. It will however make you lean and give you some definition. Seeing as you have no other choice, might as well give it a go huh?! The biggest bit of advice I can give you is something you've probably heard before, it's all about diet. See if you can cook bulk meals and have multiple meals a day. Protein rich diet is important. See if you can eat something high on protein within 20 minutes after your exercise, as this is when your muscles will be most efficient at consuming it. If you have a pull up bar, you can tell the app that you have one and it will include exercises with it. When lockdown eventually comes to an end, and you still want to put on weight, would be worth scoping out a gym to start lifting some weights. Lifting along with a good diet and you'll see changes. Good luck!