also known as "impossible music", it's so named as if you were to print out the sheet music, it would have so many notes the whole page would turn black, an example here. almost always uses a piano as the instrument, but I guess it would be possible with other instruments. I haven't seen any such examples myself

https://rateyourmusic.com/genre/black-midi/

https://m.wikidata.org/wiki/Q22964975

https://bandcamp.com/tag/black-midi much of these are actually by an artist called Black Midi though...