Agreed. This is an important safety belt that ZFS offers, and it’s baffling that TrueNAS doesn’t expose it.
I don’t know that I like the idea of automatic checkpoints on a schedule–that sounds more like something that should be handled by snapshots.
I’d add that it should come up when you’re modifying a pool–at a minimum, when you’re adding a vdev. I’m tempted to think a checkpoint should just be automatically created at that time, but at least offer the user an option to create one.