But you're not creating a new computer system, you're not designing it. You have to exactly follow the specs, and the things mentioned by parent. Seems more like mundane and housekeeping stuff rather than creative.
Implementing a well-documented spec is fairly mundane, but figuring out that spec on your own is a fascinating puzzle. Emulators are full of curious little edge cases that can drive people to the point of obsession.
So? Just because you find it boring and mundane does not mean everyone else does. For me at least, there’s few things more thrilling than learning (and maybe mastering) a new thing. You think new systems start out in a vacuum?
Besides, part of the challenge is that there is no comprehensive spec for the Game Boy, so discovery through research and implementation is part of the process.
In contrast to the creativity that you can exercise along many dimensions of implementing an emulator, riding a bike or laying at a beach with a cocktail is hardly „creative“ at all, yet many people enjoy doing that as well (I certainly do). You said you might even enjoy playing with the resulting emulator, that seems even less creative to me.
https://mgba.io/2017/05/29/holy-grail-bugs/