Sure. Comics like those from the early 20th century that no longer have valid copyrights can be found in the public domain. It gives people the opportunity to freely enjoy and even build upon those classic comics.
Yes, there are. Some older comics that have passed a certain period of copyright protection are in the public domain.
There are indeed. For instance, some comics published a long time ago and whose copyrights have expired are now in the public domain. This allows for greater access and reuse of those works.