Leg Amputee

Theoldguy1 has a good point: A physical therapist, or a trainer with solid rehab credentials, would be a good thing.

Do you still have one leg? There are people who row (boats or machines) with one leg.

You can find some exercise videos on YouTube (and elsewhere) for seated exercise. Some of them, aimed at wheelchair athletes, are quite vigorous. Speaking of wheelchair athletes, there are some places that offer wheelchair basketball, sled ice hockey, and that sort of thing; and some such leagues are open to even people with 2 functional legs who use the same equipment as the people with mobility challenges.

Have you considered an arm bike? Some gyms and physical therapy practices have them. Maybe you could try that, see if that's workable. I have no major leg mobility issues, but have been a short-endurance cardiovascular sport participant regularly for over 20 years (so not especially unfit). I used an arm bike as part of a shoulder physical therapy stint recently, and found it could get my heart rate up to a satisfying level.

Of course a variety of seated weight training exercises would be viable.

If your amputation is recent, do exercise caution: All of us are best served by increasing our fitness activities gradually, pushing to just a moderate and manageable challenge, then doing a bit more as we get fitter to always keep that challenge in the picture. While healing, it's especially important not to overstress the body (via too-intense exercise or calorie restriction, let alone both together). Keep your long term well-being in your sights!

I assume this next goes without saying, but: There's truth in that old saying that weight loss happens in the kitchen, not the gym. Exercise is great for a body, but most of us can lose weight more effectively by managing the eating side of the equation. I can burn 400 calories or a bit more in a hour's vigorous workout. I can eat 400 calories in less than 5 minutes. Not eating the 400 is easier than working it off.

In real life, I didn't much change my exercise to lose weight, either. I was the odd duck who was already athletically active (for a dozen years!) while overweight/obese. I didn't want to ramp that up much, or it would've interfered with my overall good life balance. I just figured out how to eat less and stay happy at the same time, kept up the same exercise level. That can work, even if the "same exercise level" is zero exercise. (Not that I'd discourage you from exercising in ways you manageably can. It's great for health and well being. But it's not essential for weight loss.)

Best wishes!