Download the MP3 from where? If you want a copy of a well known song, you might find one, but for something else you might struggle to find one. Your best bet is to buy used CDs and rip them yourself.
rutracker.org has many things archived
> Download the MP3 from where?
My guy, this has been solved for about 25 years.
Not everything is ripped and waiting to be downloaded…
If it's not available for download, it's not something I would be interested in :-) I understand that people are different.
The article clearly explained that this was not possible in their case.
It’s not that simple for the poster’s use case, which is “play whatever my kids want to hear while we’re in the car”
My kid is only 2 years old, but when he can understand the concept I will be sure to teach him that he doesn't have an arbitrarily large choice, he can only choose from within the options we have available.
Download MP3
Put on Plex/Jellyfin/Subsonic
Play in car
Buy MP3, download, burn CD, play in car. Kids can choose any CD that's in the car or regular radio.