@captainepoch >VSCodium is free by itself.
It's hard to know for MIT expat licensed projects, as that license explicitly allows for sublicensing, which means adding proprietary software to the project is allowed and often happens.

>Plugins are something you're not forced to install, unless you want extra features.
You're kind of forced to install them if you want the ability to compile many languages.

>You could make propietary Emacs plugins
That would constitute copyright infringement and the copyright holders won't hesitate to enforce their copyright and demand that the plugin either be deleted or released as free software under a compatible license.

Note that a privately written plugin for your personal use only is trivially free and not proprietary.