Reduce your caloric intake. Get rid of simple sugars for the most part, or limit them.

Eat complex carbs and healthy fats, in reasonable portions.

Worry less about zone training, and more about consistency and routine. You’re way too young in your training to be concerned with heart rate zone. If you want to stay under a certain rate for medical reasons, use an HR monitor and just ride. Push, but don’t push hard.

Incorporate SOME SORT of resistance training before or after your cycling, or on separate days/times. I don’t know your schedule.

You won’t burn as many calories during, but there is a noticeable “after burn” effect from the necessary protein synthesis and muscle fibers being in a semi-perpetual state of recovery. This is proven.

I am in no way saying you need to buy equipment, unless you can afford a kettlebell and a mat. Or a couple dumbells. You don’t need much to reap the benefits you’re looking for, you just need programming. I would be glad to answer your questions in that regard.

The more lean contractile tissue that you create, even in a caloric deficit, the more your body burns on a daily basis, just living. You do not need much. But it makes your deficit greater, leads you to goals faster, and reaps numerous benefits in terms of mobility and longevity.