Ok, this is what fixed it for me: remove the project folder, and clone the repo again. Why it works, I do not know.

We tested it with no react projects, and it seemed to work, but something was off in the TSX files and this is where Intellisense was bogged down. Cloning the repo fixed it after trying: clean install, cleaning all VS code folders from the Mac, and running the project in a VS without any plugins failed.