For me, in my limited experience, I enjoy LISS and mobility during my off days. Aerobics probably should be done in Zones 1-2, which you can approximate by either nose breathing while you run or being able to hold a conversation while you run. I’m a fan of footborn aerobics (running, walking, rucking, etc), but there’s also something to be said for bicycling - its minimal impact compared to the repetitive impact forces of each stride during a run, generally means less chance of soreness and easier recovery for the same aerobic intensity. Swimming is also awesome for off day recovery workouts.
Lastly, I’d imagine you can do a few easy lifts like easy sets of pull-ups on off days, but I have less experience with that.