The file permissions are looking odd. The owner ‘www-data’ has no permission to run the script because of the missing eXecution right.
Try fixing this with…
sudo chmod 744 /path/to/occ
If it still doesn’t work try to use full absolute path to occ (/path/to/occ).
sudo -u www-data php /path/to/occ update
Further information:
https://docs.nextcloud.com/server/11/admin_manual/configuration_server/occ_command.html