Maven java project in Intellij IDEA 2019.3, JDK 11.0.3: Cannot resolve symbol 'java' but still compile

Question

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 1

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