Fat loss ultimately comes down to maintaining a consistent caloric deficit, eating fewer calories than you burn.
When this deficit is in place, the body must break down its own tissue for energy, and without the right training stimulus, that tissue can include both fat and muscle.
High-intensity resistance training helps signal to the body that muscle is essential, shifting more of the energy deficit toward fat loss while preserving lean mass.
Cardio isn’t required for fat loss because its main role is simply to increase energy expenditure, something you can accomplish just as effectively by reducing calorie intake.
Still, cardio can be useful if you enjoy it or want more dietary flexibility, though too much may interfere with muscle preservation.
The most effective fat-loss strategy is a steady caloric deficit supported by hard, muscle-preserving resistance training.