alcero
Are you sure that's the correct path to the PHP executable? If you have terminal access (or SSH access) you can run something like whereis php81
to find the true path.
To make sure it's actually running you can set your Admin Panel > Settings > System > Default Log Level to DEBUG, Save Changes, wait for cron to run, and check Admin Panel > Dashboard > System Logs for a Cron Job entry. If you see a Cron Job entry then it's running. If you don't see a Cron Job entry then it's not running properly.
Cheers.