You can configure a world to not support portals, you can disable items by default, but for both it's world-wide. I think you should be able to define zones that are exceptions to those.

Example: Murder 4

I don't want people placing portals in the Mansion, but at spawn is OK.

What do I do?

This proposal lets you disable portals world-wide and then add an exception to the spawn area.

Example 2: Wide hallway

I can't get to the other side of the map without going through this hallway but some jerk won't stop putting a trampoline in the middle, making it terrible to use the map.

What do I do?

Place a VRC Feature Restriction Zone that disables placed props that affect gameplay.

This expands upon https://feedback.vrchat.com/feature-requests/p/feature-request-explicit-no-stickers-emoji-prints-portals-etc-control-zones-in-w