I did have this music bookmarked (6 1/2 hours of Commodore 64 SID Music) despite no direct connection/nostalgia to the C64. It just has something better than other retro music.

So how do I make my own SID tunes?

In most cases, you will need access to either a real C64 or a C64 emulator such as CCS64 or VICE. Ideally it is preferred that you actually compose on the real thing

I’d prefer pure midi (for use in a game engine like Godot, midi players are a fun idea too), anything where the soundfonts are free and not too big. Far down on the list for me though, and I’d probably need to lean on public domain midi files at first anyway.