Is this considered sealed?

Do knockouts have to be metal? Is this considered sealed? Main service panel. Thank you

Around here, it’s okay. It “locks” the wire from being pulled out, too.

That’s a standard push-in type NM cable connector not a knock out. The knock out is the metal slug in the hole that gets removed to allow for the insertion of the NM connector. As long as the cable installed is within the size range of the connector it’s fine.

Thanks for replying