Funny you should mention open source and VSCode.
VSCode itself, for all the promotional materials about how it's open source, is officially "a distribution of the Code - OSS repository with Microsoft-specific customizations released under a traditional Microsoft product license".
But wait, you might say, it's just like Chrome vs Chromium - so long as we have the OSS edition, it's all good! But, unless you're writing JS or TS, you need extensions to do anything useful. Python is an extension. So is C#, and C++. And all of these are partially closed source - e.g. code completion for all three, or debugging for both C# and C++.
Worse yet, the licenses for those closed source parts specifically prohibit their installation and use in anything other than the official closed source VSCode distro. And this isn't just verbiage - there are actual runtime checks in all these products that block attempts to use them in VSCodium, Cursor etc.
The same goes for the official VSCode extension gallery / marketplace - you can't legally use it from anything other than the official VSCode. Enforcing that is trickier, but even here Microsoft managed to find a way to frustrate its users: it used to be possible to download a .vsix from the Marketplace, but that feature has been removed recently, precisely because people were using that in conjunction with Cursor etc.
Much open source, indeed.