And Bach did indeed write variations on B-A-C-H[1]. But lots of composers have self-referencing cryptograms and other riddles in music. You would find far more in Scriabin, Bartok or Alban Berg for example.

It also doesn’t fit the narrative but the idea of self-reference in art didn’t start with Escher either. For example the Arnolfini wedding portrait by van Eyck[2]

[1] Bb A C B in modern notation https://en.wikipedia.org/wiki/BACH_motif

[2] https://en.wikipedia.org/wiki/Arnolfini_Portrait The artist can be seen in a reflection in the central mirror that he has ostentatiously signed his name above. It’s an incredible painting and worth a trip to the National Gallery to see if you’re ever in London.