But isn't VSCodium just a build of the Microsoft approach to OSS?
Or is that your way of referring to VSCode? I don't even think of it as OSS...

Personally, I mostly use Kate. Sometimes Vim for quick edits on the terminal or over SSH.
And at $DAYJOB, we use the JetBrains IDEs, which I hate in many ways, but they are competent IDEs, and definitely blow VS Code out of the water, if you want features.