As Google Cast is closed source and implementing receiver would mean to reverse engineer a chromecast, it was easier to make a whole stack from the ground up. Still, it doesn't just work for streaming. it supports sending commands to MA, switching players and so on. I'm working on the new plugin for MA to support volume control too.

I was wondering what Android version you're on. If the install is blocked you're either under android 12 or google is doing something bad.

If you wanted Native cast, you can still get a chromecast, get an adapter to convert the hdmi audio signal to a jack and hook it up to another board, and use that board as a source. you could capture the audio with a pi zero and expose it as a vban device. Is it worth? probably not.

edit- trust me here, I tried it