Tried to compile my favorite nonogram game (Drymouth for Game Boy Color) so I could try tweaking some mechanics, but it turns out that 26 year old code targeting a 27 year old SDK does not necessarily work well with modern operating systems.
I have been trying to make it work in a Windows XP virtual machine but there's some errors I haven't resolved yet. I also tried making it work with newer versions of GBDK but there's been a lot of breaking changes since then.
Maybe at a certain point it's easiest to just try to romhack it. There's also the option of just making my own game that plays how I want (since I don't think anyone else is going to do it), and uhhh maybe after I complete game dev projects I already have.