Desktop PC on Network cannot mirror to TV

I would use Plex for Casting. Miracast is being degraded to that devices are now going to Google Cast and Apple's Airplay as the standard. See this in how to use Google Cast. Mirror Your Computers Chromecast Yes you do have to have Chrome or Chromium. You do need to set to run in the background if you wish to have it stream all of the time.

There is also VideoLAN aka VLC that can be used. You do need to make sure that Advanced Sharing is setup properly and that your firewall allows for DLNA streaming. When you open Devices and Printers, you should be seeing the streaming device or Smart TV that you are trying to use to your computer. The cross-platform streaming solution - VideoLAN

For anything else, you would need to put media in your Public folders with no password protection on them, Search Engines are your best friend, the Google Cast threads on their forum are also your best friend.

See what I stated about Cast. You have to use Chrome or Chromium, but you can cast the desktop as long as you keep Chrome running and just minimize it. You click on Cast, then in the blue bar choose source and click on desktop. Then just minimize Chrome and you are good as long as the connection stays if you do not set your desktop or laptop to go into a sleep mode.

My wife and I use the Cast feature to show each other something that we need on the tv instead of passing the Macbook back and forth.

No problem. There is also a way to make Airplay run in Windows also. Just make sure when you mirror with Cast, that you are not running anything in the background that can hog resources.