Old way (using event force:navigateToComponent is deprecated) and new way (lightnign:navigation) is not supported in communities. How can I implement navigation?
I dont think lightning:navigation is intended for communities as the Lightning Components Developer Guide mentions:
Navigation in Lightning Experience and the Salesforce Mobile App Using Page References
you should be using force:navigateToURL:
This event is handled by the one.app container. It’s supported in Lightning Experience, Salesforce app, and Lightning communities. And this is for navigating in between different community pages.
If you need to "switch" from one componet to another, you will actually have to manage the rendering and use lighting Events.