Note that this feature doesn't work in open source builds of VSCode, it's an MS only thing.
A FOSS build is available at https://vscodium.com/
By packaging it as an extension that isn't licensed like the rest of VSCode.
Also on a related note, if you're using an open source build of VSCode (such as VSCodium) then you cannot use marketplace.visualstudio.com/
https://github.com/VSCodium/vscodium#extensions-and-the-mark...
They want Theia to be a tool to build your own editor and it can be built as a hosted solution (like code-server) or a standalone editor
Edit: I see that the article also mentions Theia but this point about Theia vs VSCode is not mentioned.
https://github.com/VSCodium/vscodium/blob/master/DOCS.md#pro...