1, view the project’s jdk (Ctrl+Alt+shift+S)
File ->Project Structure->Project Settings ->Project

2. view the jdk of the project (Ctrl+Alt+shift+S)
File ->Project Structure->Project Settings -> Modules -> (the name of the project needs to be modified) -> Sources ->

3. View Java configuration in idea
File ->Setting ->Build,Execution,Deployment -> Compiler -> Java Compiler

If the above three steps still fail
Clear IDEA cache Restart IDEA
File->Invalidate Caches/Restart