When I use Rider I just fully accept that it's not open source. Same with the old Visual Studio.
VSCode on the other hand looks open source, they claim it's open source, the extension is open source, yet the most critical component is not. I would call this the new new Microsoft - we look like we love open source, we give you open source tools, but it's either not open actually (this) / will not work if you compile it yourself (VS Code and .NET debugger) / only works on Windows ("Multi-platform App UI", maybe Mac, I don't know)