Hello, I still use iTunes.
The latest macOS offers the world’s best way to play — and add to — your collection of music, movies, TV shows, podcasts, audiobooks, and more.
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I mean, it has its issues, but i'm buying from apple. Most of the files I purchase on there are coming down in mp4 these days, which was not around when the Tahoe was built. I've been using iTunes since 2000 or so when I was still using my iPod (which would play through the aux port). Honestly, I would love to find another solution. I recently picked up my 2009, and so I've been trying to make things work with that older tech. I have picked up Foobar2000 (
https://www.foobar2000.org/) which converts my other (modern) formatted songs into mp3 (that the Tahoe can play) and does it in batch. With that I can fit about 69-70 songs on an mp3 CD that plays in the Tahoe. I use an m3u playlist from iTunes, and the songs are under the folders by artist, album, as they would be on my pc. After you use Foobar2000 you have to edit the file extensions to mp3 in the playlist file. I know that goes beyond what you were asking.
If I didn't still have iTunes, I might try Shazam, which I use to figure out songs that are playing. I also think Amazon sells digital music, or did at one point. I'm also very open to suggestion myself.