I am starting to develop mods for Sims 4, and I was hoping to use examples to learn. The broadest mod I can think of is MC Command Center.

How can I decompile MC Command Center's .pyc files?

I have tried the following:
- unpyc3.py
- uncompyle6 library

You can't decompile MCCC, it's done that way on purpose because people were stealing from him. You could try to find a really old version before he implemented this change, but it's been several years and the code will be outdated in some parts. I would recommend looking at other mods instead and if you have questions, join the Creator Musings server linked in my signature. There's modders and resources there to help with your questions (there are no scripters who frequent these forums enough to catch any possible questions).