Thanks to this Hackaday article, I found a video describing how to use Visual Studio Code to write 6502 assembler for the Commodore 64!
It’s been a long time since I’ve done any ASM on the C64, and compared to the programming environments available these days, I was working in the dark ages with my Action Replay monitor, typing code directly into memory.
Kick Assembler is used to assemble the code into a .prg file, using the KickAss (C64) extension for VS Code to launch the emulator with the code loaded into memory. I see Kick Assembler 8-Bit Retro Studio is mentioned in the comments, and it is indeed still being developed, so it might be the better choice, but either will make developing on the C64 much simpler.
It gives a nice overview of using Git to track changes too, something I would have also loved on the C64. So many files prefixed with numbers as I experimented with effects …