Yes and no.

Doing pull-ups will make you stronger, but it’s lats and biceps, if you’re wanting to be a boxer they aren’t the most important muscles to target. Also at a point you’ll be training endurance not strength. You’ll need to add weight to overload.

Losing fat through cardio. Ehhh… like technically yes. Practically though not really. It’s really hard to out-train a bad diet. Losing fat is something best done in the kitchen not the gym. Problem is losing fat requires a callorie deficit, and gaining muscle requires a surplus. It is possible to do both but you’re really fighting biology. Do do cardio though - it’s its own benefit. Better lungs and heart is so important for everything else.

Yeah training will work endurance. Much like strength. But the way you train for the two is different. You can train both but again it’s non optimal.

The good news is that as you’re just starting out the gains should come easy so you don’t need to be optimal just yet. Keep it up and decide what you want to be your goals. Then build a focused training plan for those goals. You don’t have to do it forever either. You can initially try lose fat, then pivot into strength training, then pivot into endurance or back to fat loss or whatever suits your goals at the time.