Everyone can agree on VLC being the best video player, right? Game developers can agree on it too, since it is a great utility for playing multimedia in games, and/or have a video player included. However, disaster struck; Unity has now banned VLC from the Unity Store, seemingly due to it being under the LGPL license which is a "Violation of section 5.10.4 of the Provider agreement." This is a contridiction however. According to Martin Finkel in the linked article, "Unity itself, both the Editor and the runtime (which means your shipped game) is already using LGPL dependencies! Unity is built on libraries such as Lame, libiconv, libwebsockets and websockify.js (at least)." Unity is swiftly coming to it's demise.
Edit: link to Videolan Blog Post: https://mfkl.github.io/2024/01/10/unity-double-oss-standards.html
You CAN access the source code, but it's for corporate/enterprise partners. afaik
Charging for access is actually fine under L/GPL but after that you're then free to redistribute at your own price. I imagine Unity heavily control how you use and distribute your modified engine (nonfree).