What is "dumb"? What is "intelligence"?

I think, as long as people have normally functioning brains, it is possible for them to understand. And I think nurturing critical thinking is an important aspect of how to approach this.

You can absolutely present a complicated topic to someone who isn't educated in that field, or even has low education at all, if you are being humble about how you explain it and try to meet them at eye-level.

You don't need to give definitive answers, you may give recommendations, but you can always explain a bit and note that there is also a lot more to it than what you explained and that one must take care before making some further conclusions.
Interested people in your audience then have some first basis and grasp of a topic and can take it up on themselves to dive deeper; for example, by asking questions or finding further sources (you might refer them to these).