Oh boi! I'm close af!
One more resolution and it will be a success!
Once I got the correct resolution, I will release a template.
Also, I can't send you Mii Maker save file since it somehow connected to the NAND file. But I'm not sure.
Edit: Welp. Mii Maker won't scan QR Code. No matter what the resolution(720p, 1080p, 4K), it will give us this low resolution image.
On the bright side, other games won't have this issue somehow like Digimon or Pokemon.
See https://github.com/citra-emu/citra/pull/2412, mii maker requires not only a functioning camera, but also Wrap/Unwrap implementation. I am working on it