The 6502 processor has a special place in the childhood memories of many of us, because in the 80s it was at the heart of many micro (and not-so-micro) computers. The Apple II is probably the most iconic. But not one of the best, honestly, and for many of us the real winners were Vic-20 and C64: “the” 8-bit home computers, together with ZX Spectrum.
6502 Assembly is a good start if you want to play with bits, bytes and registers. It’s easy enough not to be intimidating, but it’s a real Assembly with actual potential applications. And there’s plenty of online courses to learn it, even if most of them are focused on retrogaming platforms like Atari VCS and Nintendo NES.
It’s also a good way to learn “programming with limitations”, since old systems of the 80s didn’t offer much in terms of digital resources. That said, there’s plenty of room for improving your low-level programming skills. And then jump to more complex platforms.
It could sound a bit esoteric, but there are different ways to emulate a 6502 processor using simple SBC boards - kind of obvious: a modern board controller is more powerful than a 6502 chip. With a good emulator and a good SBC, you can have a little portable retro machine, customized for your own digital tastes and ready to play your own games (why not?).