With extensions it can be. And if it would be built on a custom GUI framework, it could not.

Rich IDE is not something you achieve by slapping a few extensions on an editor. It's in the name - Integrated. It means that there's a GUI designer which is aware of local classes, inspector at runtime which can jump into the right areas of code, performance analysis that gets populated during runs, highlighting and compilation that's aware of the currently selected configuration, etc. There's an extension a few of those, but they're mostly independent and isolated.

Codeblocks is an IDE. VSCode is pretty much on par in terms of features.

It's a spectrum. I'd give codeblocks 25% of an IDE ;) But it will depend heavily on what you expect.

At least comparing to Eclipse in terms of Java support, VSCode is still way behind. I've been using it almost exclusively for maybe a year, since I was mostly working on JS and Groovy code, but now went back doing Java dev on Eclipse, and it is a significant difference.