What I have:
– Intellij IDEA 2019.3, bundled JDK 11.0.3
– A Maven project with project JDK: the bundled JDK

My problem:
For any java. imports I get the error Cannot resolve symbol ... but I can still compile correctly.

I’m totally aware that a lot of people already discussed this problem, and of course I have tried all of it:
– Use the dialog ‘Setup JDK’ a thousand times to set the project JDK again
– Validate that all modules and the project use the correct language level 11
– Invalidate Cache / Restart
– Delete the file <project name>.iml
– Delete the .idea directory
– Reimport the whole maven project

Answer

The problem is connected with the bundled JDK: I have installed manually another JDK 11.0.4, set it as project JDK and now it works