As a example: Rider (https://www.jetbrains.com/rider/) - a IDE - comes with everything you could possibly need to build and compile .NET apps out of the box, while VSCode - a code editor - relies on extensions (and thus mostly the community surrounding VSCode) for this.

Or to make things more succinct:

* VSCode is a extendable code editor (like vim, neovim, Zed and Sublime)

* Jetbrains Rider is a fully equipped Integrated Development Environment (like Microsoft Visual Studio or its direct sibling Jetbrains IntelliJ IDEA)

And while extensions are optional within a IDE (and often solely used for increased productivity), more often than not they are a necessity in a code editor to even become productive.