Fixed in 2021.1, please see https://youtrack.jetbrains.com/issue/IDEA-135546
What was that?
All IDEs based on IntelliJ platform have a global setting telling whether to treat file systems as case-sensitive. The setting depends on OS: by default, Mac OS X and Windows are case-insensitive, Linux and friends are case-sensitive.
You can either move your projects, or tell an IDE to change it's its mind.
For the latter add the following line to IDE_HOME/bin/ idea.properties file (Help | Edit Custom Properties, see "Configuring platform properties" for more details):
Use true if your projects are located on case-sensitive FS, false otherwise. Then choose File | Invalidate Caches and restart the IDE.
Nope. Setting the global property is a temporary solution; vote/watch this issue to be notified when a permanent fix will be in place.