How is Multiplex actually implemented?

Hello,

I am studying networks for class and I've read about Simplex, Half-Duplex, Duplex and Multiplex.

Now as far as Simplex, Half-Duplex and Duplex go, I see them as how two partners communicate. They're pretty easy to understand on their own.

Multiplex I would define as how to share a medium for communication like time-division multiplexing, space-division multiplexing and frequency-division multiplexing.

But I have a few examples in my head where I just cannot really make the connection, if there is any

1. Radio: For radio to work the way I see it we would combine Simplex and Multiplex. My question: Wouldn't many listeners connecting to the same radio station over the same frequency cause problems? (Maybe I'm thinking too much from a wired perspective)

2. Broadcasting-Pattern: The way I understand this, this is a case where we have Multiplexing and Half-Duplex. In a scenario where a participant in a LAN would want to resolve an IP to a MAC-Adress it would have to communicate via Broadcast, where it sends while every other participant listens. Now I see two ways to do this:

A: Every device is connected to every other device or B: The request would be sent to the Layer 2 switch which then communicates with every other member in the LAN.

This leads me to the next question: Using Switches as an example, is multiplex generally realized by using a parent-node (say a layer-2 switch) to connect one participant to multiple other participants at the same time?