Light cardio on rest days is fine and can aid recovery, but keep it easy so it does not eat into muscle recovery.
Yes, easy cardio on rest days is a good idea for heart health, calorie burn, and blood flow that can actually speed recovery. Keep it low intensity, like a brisk walk or easy cycling, so it does not add fatigue that competes with your lifting recovery. Avoid hard intervals or long grinding sessions on rest days, since those tax your legs and nervous system and turn a rest day into another workout.
A brisk walk or easy bike ride pumps blood to sore muscles, delivering nutrients and clearing waste, which can reduce soreness. This kind of active recovery leaves you fresher for your next lifting session rather than more beaten up.
The point of a rest day is to recover, so hard HIIT or a long run defeats it, especially for your legs. Keep the effort conversational, roughly zone 2, so you get the benefits without adding meaningful fatigue.
Large amounts of intense cardio can blunt strength and muscle gains through the interference effect and by adding to your recovery debt. Light, moderate cardio does not, so keep the hard conditioning to a couple of dedicated sessions, not every rest day.
Light cardio on rest days is fine and can aid recovery, but keep it easy so it does not eat into muscle recovery.
