Welcome! This forum has a treasure trove of great info – Scouters helping Scouters! Just a heads up, though - all content, information, and opinions shared on this forum are those of the author, not the BSA.
The issue was that for youth protection rules, dens often need to invite other pack leaders to fulfill two deep leadership. So, they were added as an option.
I would selectively invite adults, then duplicate the event using the Extension’s Copy Event button to create the next one. That preserves your invitee list, and allows you to just fiddle through changing the details of the event. You can safely use Select All to update scouts and parents invited to the meeting, without disturbing the leader invitee list (e.g. if scouts join or leave the den).
It’s not clear that subdividing the leaders into “Den Leadership” and “Not Den Leadership” is a near-term change. The subdivisions are part of “native” Scoutbook, rather than part of the extension. It took a while to get the change made to offer the option of inviting more than just the adults assigned to the den/patrol as leadership. Another reasonable proposal for modifications to the calendar recently got a response that the calendar is being rewritten, and they would pass along the request to development.