Some apps still working is because the authentication is not mandatory.

Screenshot from Tweakers.net discussion:

We have a Chromecast 2nd generation which has indeed the known problem. However when I use Music Assistant from Home Assistant I can cast from my own music collection (flac files).

I haven’t tried yet to cast from Spotify using Music Assistant.

I own an iPhone and casting a Youtube video indeed doesn’t work. This results in receiving an untrusted device message.

Questions now coming up are

• why are some apps still able to cast to a 2nd generation Chromecast?
• are there more apps still working?