If I remember correctly, the NZXT CAM app is built on a mixture of C++ and C#. If that's the case, I cannot understand for the life of me why this app's UI is still so horrible.
Here's some documentation links:
WinUI 3.0 | Overview
WinUI 3.0 / Windows App SDK | Microsoft Docs
Microsoft's Fluent Design Principles
Includes links for the new Segoe UI Variable font, Figma toolkits, samples and more.
XAML Control Gallery
This is Microsoft's primary sample app for the new UI controls moving into Windows 11 (and Windows 10 v21H2.) Every single control has a page with multiple examples, covering multiple use-cases, with both excerpts of code and links to the full code (hosted on GitHub, completely open-source.)
Please let me know if more links are needed. It's 2021. This app feels worse than the first public distribution of Electron.