Another reason why physical copies and sailing the seven seas is always a viable option...

For even more context, I have an Android phone, a Note 9 to be exact and Google Play was basically the default way to play music on the device; bascially Android's iTunes. I can tell you that even before this I've had mp3s I've downloaded & put in playlists disappear at random.

This isn't Google's first time forcing people's hands into or with YouTube's black hole of even less content freedom. (See the old Google+ account thing)
I'm all for supporting the original content creators so do so & with as few middle men as possible.

And yeah, sometimes sailing the seven seas becomes the only option. Digital for convenience but physical (& digital w/o DRM) for keeps.

Ok, more clarification about this..
a) yes, you can transfer to YT Music, as I did
b) sadly from what I've & others seen, stuff gets lost along the way
c) It's Android, so there's a bunch of alternative players
d) Big G should have made it offline instead of forcing YT Music

...e) the point still stands that you should be mindful of digital & analog content preservation.

f) I'm a programmer (who has worked with Google actually on new products)..the way they went at this was rather forceful & inconvenient.
g) For many it'll be an ok transfer...

...but it should have been done better. Google has a tendency of forcing people's hands on their vision when they make, break or forget things (see aforementioned Google+/YouTube account debacle from years ago).

Oh & about "sailing the seven seas". Generally, don't do it if can be avoided. Like I said prior, support content creators and try to find as few middle men in the process as possible (heard bandcamp is great). But sometimes industry will stupidly make it the only viable choice

(Bonus) People who paid for Stadia right now are like..