A gentle walk in a quiet area with good soft healed shoes should be OK. I mentioned this before. Put foam ear plugs in so you can hear your foot falls/foot plants. You will hear the impact intensity your foot plant transmits to your brain. Then you can learn to take softer steps to cause less jarring to your head.

Do not walk for aerobic exercise. This is to get some fresh air and some gentle blood flow going through your brain and body.

Walking on grass should be easy on your head. Or an artificial surface running track.