I spent a whole summer learning under a music producer that went to my college. One of the most useful exercises that we did together was taking a basic song and simply trying to recreate it without any tutorials. You can look up the BPM and the key of the song, even the chords if you wanted to, but everything else is up to you using your ear to figure out what sounds are going on.
The guy I was working under used EDM as an example. This helped me learn the basic structure of EDM, how to program drums for EDM, and even helped me sharpen my sound design skills.
What I'd recommend to you is to follow a chiptune tutorial and recreate what they do to a T (this will help you understand the basics of composing chiptune), then take a chiptune song you like and try to recreate it without a tutorial. Just use your ears and see how close you can get to the original, cross-referencing it as much as you can without finding a tutorial for that song.
From what I understand about chiptune music, at its core, it uses the most basic waveforms due to the restrictions of older consoles. For that, I recommend a couple VSTs that specialize in chiptune.
- Magical 8bit Plug
https://ymck.net/app/magical-8bit-plug-en
- NES VST
https://www.mattmontag.com/projects-page/nintendo-vst
These helped me out a lot when I dabbled in chiptune. If I recall correctly, they were also used in Undertale's OST, so they're perfectly capable for video game music.
Sorry for the word vomit, but I hope this at least helps a little bit.