Just doing more exercise doesn't actually help much with losing weight, as it turns out. The human body will optimize around even intense exercise to reduce calorie burn to a homeostatically stable level. The exercise will still make you healthier (and have some marginal extra calorie burn from e.g. extra muscle mass), but you'll only lose serious weight if you also reduce what you eat.

There are a bunch of articles out there about it, but Kurzgesagt has a decent pop-science summary: https://www.youtube.com/watch?v=vSSkDos2hzo