Maybe you already know about LibGen, sci-hub, and archive.org. Or maybe not. But now there’s a one-stop-shopping site for many forms of electronic media: https://annas-archive.org/
This is all thanks to Emil Kierkegaard (no relation to Søren). Details and examples from Emil:
For music, the Petrucci Music Library is great. Access to commercial recordings requires a subscription, which is cheap.
https://imslp.org/
Information wants to be free (or almost free), amirite?