This device reminds me of https://en.wikipedia.org/wiki/HitClips (also worth reading: https://hackaday.com/2022/01/10/hitclips-custom-cartridge-ha... )

It's unfortunate that "always offline" needs to be added, as that would be the norm 15-20 years ago when portable media players were at the peak of their popularity. You can still buy SD/TF/microSD players at a very, very low price today.