Hello and welcome to the forum,
You’re not the first, and definitely not the only one wanting ‘real life’ color mixing in Krita. Also, not the first to think Mixbox is a good and convenient solution.
Here some topics discussing Mixbox in specific:
Mixbox for Krita!
Implementing MixBox mixing for Krita
Resume: Mixbox has incompatible license and probably will never be implemented in Krita, as stand right now.
The alternative, which already has the heavy lifting done from what I understood:
I realized the spectral mixing of mypaint in krita
Cheers