Nice to see that it's not just another VS Code spin off. They seem to be finding a nice middle ground between the very basic Arduino 1 IDE, and an over-complicated all-in IDE.
What? That’s exactly what this is. Theia is a fork of VSCode that Eclipse maintains (with a slightly differently structured backend, I think), and they’ve forked that and removed the bits you don’t need for working with Arduino. You can see it in the screenshot, it looks like VSCode with less buttons.
you cannot have full intellisense on Arduino project because of how the pre-processing works and generates headers and forward declarations.
IDE 2.0 contains a Language Server developed from scratch to handle this, and every platform supported by ClangD works.
Even using the Arduino plugin for VS Code won't offer proper completion, hinting and jump-to-definition