A deload is needed more when volume is higher and you’re pushing for progress every workout. When fat loss is the goal, volume should purposely be reduced a little and you’re shooting more for maintenance (maybe with the occassional progress) rather than constant progress. Now if you’re going to be in a deficit for a while, sure… I can see taking a diet break when needed and possibly using that time to deload as well if it felt needed.
What does a HIIT workout look like? You could jog for two minutes, sprint for one minute, jog for two minutes, sprint for one minute. Or you could do a HIIT workout on a bike, or by running up stairs and then jogging back down. The key is that you go relatively all out for a short period of time, then recover by maintaining a moderate level of intensity, then go again.