While it is true that the body burns fat during low-intensity workouts, the fat burning rate remains low and you have to exercise longer to burn the same amount of calories you would at higher intensities.
In a high-intensity workout, although your body uses your glycogen stores first for 'fast energy', it depletes the glycogen stores rapidly enough to force your body to tap on the fat storage. This means that high-intensity workouts are more efficient in burning way more total calories – both glycogen and fat calories. Ultimately, the total number of calories you burn leads to the most weight (and fat) loss.
https://www.mountelizabeth.com.sg/health-plus/article/fat-burning-zone-heart-rate-to-lose-fat