Sometimes for unkwown reason intellij hang on and lost symbols and made a remark that say "cannot resolve symbol XXXXX", but the symbol exists and compile. In order to resolve this problem you need restart cache of intellij
If not works you can delete the hidden folder .idea of your project and restart the IDE
Ctrl + Tab: Switcher
You can find your plugins installed in the following path:
~/Library/Application Support/JetBrains/IntelliJIdea2020.3/plugins
Where <IntelliJIdea2020.3> it's your IntelliJ/JetBrains product
More info about this in https://www.jetbrains.com/help/idea/tuning-the-ide.html#plugins-directory
