You have hundreds of options for devices like this. Amazon alone shows 200, or well over 300 if you don't need live internet audio streams.

You're about to respond: "But many of these use Android, and general purpose computers are too distracting for me." In that case, you'll need to forego live internet audio streams and buy a closed option with a radio receiver.

> I would like an audio device which can play mp3, podcasts, internet radio.

Get a second-hand Apple iPod Touch, remove all apps you don't need.

For just mp3 and podcasts: get an iPod Classic (or Video) and install Rockbox.

Rockbox is amazing.

> I would like an audio device which can play mp3, podcasts, internet radio.

That internet radio is a whole magnitude of complexity, especially with the need for wifi (cellular?) if it needs to be portable. But there are options like specially modified android devices.

I have the Shangling M0 with a 512GB card. I don’t even bother with converting my flac files. A nice other device is my kobo. It holds my entire fiction library with space to spare.