How to do upper body workouts with leg injury?

Hello, recently I got stitches on my knee and am not allowed to do any lower body workouts as I cannot bend my knee

Usually for upper body I follow along and do them standing just like shown in FB videos. I have been in the FB community for a long time, so I am not new to any of the upper body exercises

How can I now modify my upper body workouts by sitting? Did FB make a video or article regarding this? I don't have a bench. I know I cannot do pushups or tricep-dips as I cannot bend my knees

Edit: I know I can do kickboxing on a chair without moving my legs, but I am asking specifically for strength-training