Little skulblaka in backwater USA knew about dragons, but I had never seen one before or successfully convinced anyone that they were real despite a wealth of unrelated cultural works depicting them.

If I were asked to make up some numbers about it, I'd expect that maybe 60% of the galaxy had probably heard of a Jedi before. But none of them had ever seen one or met one. Nor had anybody they knew, or anybody those people knew.

People like Han Solo who frequently travel between planets and systems would probably be more likely to run into someone who had actually had dealings with a Jedi before. But also, maybe not. Han mostly runs with lowlifes, while Jedi usually interact with major story protagonists and/or antagonists, government officials and Sith and the like.

So it's entirely possible that 'everybody' knew about the story of the Jedi, but they were so rare that most systems would go generations without ever interacting with one. Unless that system was involved with the Sith directly, in which case they probably have been told in briefings that the Jedi are both real and likely incoming, and also in which case many of the citizens of said system may not live to escape and tell anyone else about being rescued by Jedi.