Forum moderation permissions should not be available for the Global moderators group, as they have no effect.

This topic says it all. https://www.phpbb.com/community/viewtopic.php?f=46&t=2167023

The ACP appears to allow you to set Forum moderation permissions under Groups forum permissions for the Global moderators group. However, these permissions have no effect because the Global moderators permissions are, global. So, no reason to display them and it is confusing to do so.