I wondered if you could use a modern encoding, like QAM, on these things to improve the sound quality. It would be digital and need an external decoder, but ok.

Then I found someone had tried it… https://electronics.stackexchange.com/questions/596747/how-much-data-could-be-stored-on-a-standard-compact-cassette-using-modern-encodi

Music aside much of my childhood was focused on obtaining cassettes as one could cram a whole treasure trove booty of games onto a single cassette.