For me, VSCode keeps screwing up file encodings in a legacy project i maintain. I tell it not to autoguess the encoding and define a specific encoding to use. VSCode ignores that and keeps autoguessing.
VSCodium honors the settings (and is a wee bit more private and open-source).
AFAIK you can download every extension as vsix file from vs code web marketplace and then import it into VSCodium. That's how I have been installing missing extensions so far and it works well.