You can 100% continue to purchase content and add to your library. Just because the apps have split (as they already have on Apple’s own platforms), does not mean you can not download purchased content or continue to purchase new content for download.

https://support.apple.com/guide/music-windows/build-your-music-library-mus0f01bdce4/1.4/windows/10

Buy music from the iTunes Store If you don’t subscribe to Apple Music and you want to add your favorite songs or albums, you can buy and download music from the iTunes Store. And if you previously purchased items from the iTunes Store, you can download them to your authorized computers and devices (up to 10 total).

I also listen to music a lot outside so I have to own the digital version too.

Why, are you not able to stream it?

CD is become more rare anyway.

I'm not sure that's true. Are there numbers you can point to to back that up?

flexibility of digital music locally

I can make Spotify store locally. It's really weird how fast that is come to think of it. Very useful for patchy data. Easy to skip tracks you don't want as well.

bring my music everywhere

I use Spotify but I think ITunes does similar. I feel strongly about Apple products though so I've no experience.

I'm also not an audiophile

Although this has no impact on streaming or use of temporary downloads, or any relevance to your need for purchasing audio files, I am what many would refer to as an audiophile.

I have worked as an audio engineer in music recording and post production, I own professional audio reproduction equipment and I make my own music as a hobby.

Even so, being able to throw on a favourite album, old or new, while driving or at the beach or a friend's house, is to me akin to magic.