After back surgery

Are you working with a physical therapist? FWIW you don't need to exercise to lose belly fat because you cannot spot reduce. You can essentially lose weight with calorie control. Since you still hurting even after your back surgery you may need a doctor's or a physical therapist's advise before doing any exercise.

I've had 4 back surgeries, last big one was two surgeries for a double inter body fusion. I do my PT exercises and added more stretching and strengthening ones from Yoga with Adrienne and Sidney Cummings. I only do half sit-ups and bird dog poses in my yoga routine as far as strength. I also lift weights and am currently doing seated cardio because of nerve damage in both sides from the waist down that's really flared up. Before the nerve pain got worse I was able to do various low impact cardio, I started walking in a pool then riding my recumbent bike which has great back support. If you want YouTube video recommendations send me a message, I have a bunch from the last few months.

Maybe consider yoga and/or tai chi, or even pilates. If you're capable of those HIT sessions, do them, too. Don't limit yourself to one type of exercise, though. Bottom line, it sounds as though you need to work on form and core more than anything else.

To lose fat one must eat fewer calories than they burn.

As an adult who can't run because of knee issues I lost 20lbs in 2.5 months with CICO and my kickscooter (kickbikes are even better). I love taking mine out on paved trails and typically ride anywhere from 30 minutes to 2 hours. Kickbiking is a super low impact exercise that burn the amount of calories somewhere between biking and running. Make sure to alternate kicking legs every 4-8 kicks for an even workout and to kick with propper form to spare the tendons in your ankles (heel-toe works best for me).

Swimming.. And control your diet. 80% of weight loss is what you put into your body

I have had two spine surgeries, both multi-level (cervical C3 to C7) and a 6 level thoracic fusion. I also have lumbar issues (not bad enough for surgery but painful). Definitely connect with a physical therapist and possibly a massage therapist as well (best pain relief I have found is via massage therapy). I have had to change up the way I exercise. Walking is painful to this day, so I limit my walking time for exercise. The best cardiovascular exercise I have found is lap swimming ( pain free so I am able to swim up to an hour a day. If you add flippers and an exercise board, you can really work your core muscles, build strength in your abdominal and back muscles, strengthen and tone your leg, arms, and shoulders, increase your range of motion, and gain flexibility. I do most of my stretching in the pool because it is pain free and safe. You can connect with a PT who knows water therapy or look online for good exercises. My second favorite exercise is riding my bicycle for 40 to 60 minutes per day. Another great cardiovascular exercise which builds core strength and balance and strengthens legs, glutes, and body. Be aware of what feels good for you and what causes discomfort and pain. It took me a while to realize that not every PT is skilled enough to adapt their standard exercise plan for a client who is no longer average. I still do PT exercises, but break down the program so that I am only doing one or two per day instead of all 10.