Wording should match the options. The text says "when off" and "when on". It should match the options beside which are "Yes" and "No". Inconsistent words could be slightly confusing especially for new admins.

Requesting the words describing the item be altered to match the options that the admin picks.

Quote from Server Settings in ACP:
Run periodic tasks from system cron:
When off, phpBB will arrange for periodic tasks to be run automatically. When on, phpBB will not schedule any periodic tasks by itself; a system administrator must arrange for bin/phpbbcli.php cron:run to be run by the system cron facility at regular intervals (e.g. every 5 minutes).
Yes No

My suggestion on how the wording should be changed:

Run periodic tasks from system cron:
When set to No, phpBB will arrange for periodic tasks to be run automatically. When set to Yes, phpBB will not schedule any periodic tasks by itself; a system administrator must arrange for bin/phpbbcli.php cron:run to be run by the system cron facility at regular intervals (e.g. every 5 minutes).
Yes No

OR, change the Yes/No options to On/Off, you decide. Just be consistent.