I've read it, but I don't really understand the legal issue. I'm also not sure what could be illegal about VSCodium. It uses the Open VSX store for downloading extensions (but not every extension is on there).

It would certainly be better if VSCode was under a Copyleft license, so that it couldn't be turned into proprietary software and maybe that way addons would also have to be Free Software, like in Blender. But Microsoft clearly doesn't want that.

I’m not much against having repositories with plugins, extensions or whatever BUT they should be like Debian, you can just pack everything into images / a folder and use offline for ever when required.

Yeah, that's a good idea. They could also just be added to Debian, which would solve this problem, but there also would be another benefit for me. Most people don't care about that, but I want to only use Free Software. When I install something from Debian's free repository, I don't have to worry that it might be proprietary, because they only allow Free Software there. I don't have this certainty when installing software from most other places.

Same goes for modern Docker powered solutions and JavaScript frameworks.

Some JavaScript frameworks and libraries seem to be packaged in Debian. But most people use NPM, of course.