1) You can also setup what to Sync in MMA in the Sync settings, but I find this much easier done in MMW. Note that you don't need to connect via USB to set this up. In MMW4 you can access the Device Profile through the Options when the device is not connected.

2) Cast can cast to any Chromecast or DLNA capable client. Are you sure the TV supports Chromecast? Screencasting tends to use Miracast instead.

Ok, I think I've got it. Previously I wasn't connecting my phone via a USB cable, only WiFi. Now after connecting my phone via USB, selecting the playlists I want to sync, I can now use the 'Sync now' feature to update the previous selected playlists.

How is the 'Cast to' button suppose to work? When sitting in front of my TV, which I have a Google Play attached, MM reports No cast device. If I go to my Pixel 6 Pro setup screen and turn on screen cast, I see my phone screen on the TV, and MM sound comes through the TV.

You pick what is Synced in the Device Profile.

I know this is a really stupid question, but how do I pick the particular content to sync from my music library to my Pixel 6 phone? Of course, I don't want to synch my whole library, just specific playlists or songs.

I have my phone all setup and connected to my computer with MM on my phone telling me everything is in sync. Select sync server shows my desktop and local IP address.