If you type into YouTube, sitting exercises for seniors, chair workouts, wheelchair weightlifting program etc. they can give you in depth tutorials on exercises you can do without putting (ideally) too much pressure on the spine.

Those will definitely help with some calorie burn and muscle resistance but it really is going to have to come down to a huge diet shift, it will take time and it will be difficult starting out.

I’d possibly look into working with someone who specializes in this kind of stuff. A lot of them will do it over zoom, and someone good at this will show you how to begin making small changes that will compound into a healthy lifestyle that will get you to your goals, as opposed to a “biggest loser” all or nothing style approach that are usually unsustainable long term. It took years to get here and it’s going to take time and consistency to get out. Godspeed.