Personally I cycle, I also have bad knees and I do think it's easier on them

Oh, there are sooooo many types of exercises! Search and try things YouTube can offer. I sometimes do the smaaall morning routine- stretching neck, moving shoulders, waist, hips, knees and ankles. It takes like 5 mins, but feeling rest of the day like -15 years. It's impossible to call them exercises, just a minimal movement. Like they did at school years ago before starting classes.

Good news! Exercise helps against depression! Biking is a very good way to get moving if you have other health issues. I’d also look into swimming if you have access to a pool (or a lake or ocean where it’s safe to swim).