ACP > General > Server configuration > Server settings
The explain text for "Run periodic tasks from system cron" is wrong I think (see bolded portion):
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).
This is at variance with the Wiki and at least in my testing it doesn't work
You might want to link this to the Wiki but it should probably be more like cd "/path/to/board"; ./bin/phpbbcli.php cron:run. Based on my testing so many forums are using shared hosting that multiple commands in a cron are often not allowed so perhaps it should have a caveat for dedicated or virtual hosting. My solution for shared hosts which I've tested is in the Wiki.