I have chronic pain as well as mobility issues. I use an elliptical exercise machine that is used while seated in a chair. It helps burn calories and sculpt the lower body. It also helps circulation and mobility.

Chair exercises with weights and resistance bands and getting in the pool and walking or swimming or doing the water aerobics

I like to sit in a chair and lift my legs like I am marching. My goal is to get my knee as far up as possible. And I usually pump my arms up and down or swing back in forth. Walking is a close 2nd.💪🏼

I've heard it's Walking as much as you can at a pace that works for you.

I am a plus sized health and fitness consultant... any workout can be done with modifications as needed... depending on how long it's been since you have engaged in any real fitness activities.
In my plus sized accountability groups we start with short walks while we focus on nutrition usually for 2-3 weeks to help them start building healthy habits.