M365 Group guest access permissions in Admin Center don't work

Note the following description for "Let guest group members access group content":

If you don't select this, guests will still be listed as members of the group, but they won't receive group emails or be able to access any group content. They'll only be able to access files that were directly shared with them.

I can confirm that my test guest external user no longer receives emails sent to the group DL, but they are still allowed to send emails to that DL. That should not be happening, but it's a minor annoyance for now.

More importantly, the default Documents document library that's created in the SharePoint site for the M365 Group (and documents within that library thata weren't specifically shared with that user) is still accessible to my external user, even after I unchecked the second option (still checked in my screenshot). Do the permissions require time to propagate (it's been over an hour)? Or what other "group content" is meant that's under this permission's control?

Solution 1:

It was a permissions propagation issue and started working shortly after I posted this (of course). It works as expected.