I used this version Armbian 23.02.0-trunk Bullseye with Linux 5.15.90-flippy-81+o.
I solved the crontab problem by this way.
1. create a file under the folder /etc/cron.d/ , such as [ vi /etc/cron.d/rebootvms ]
2. write the crontab job, such as [ 1 1 * * * root /usr/sbin/reboot ]
3. restart the crontab service, [ service crontab restart ]
done!