[esclerofilo]

> Is VSCode really all that "controlled by Microsoft"?

Yep. VSCode "core" is open source, but many of the official extensions aren't (Python, C#, Live Share, Dev Containers IIRC). Besides, accessing the extension marketplace from a non-official vscode build is against their terms of service, meaning forks like vscodium don't have easy access to most extensions.

[bluish29]

VScode official build is not open source. They take the open source code and apply some stuff related to their proprietary extensions and product and then release it. And as you said you can't use their proprietary extensions or their extension marketplace endpoint (legally at least) outside their official build