Friends unable to join eachother's worlds

I am on PC and cannot join my friend's world that he is playing from on the switch. I can see him online and received an invite for the world and have tried to join many times. I have tried many different fixes with my router and with the minecraft app on my computer and with his on the switch but nothing seems to work. He cannot join my world either. He received the invite and can see me online, but cannot join me. We both get the attached error, even though we have tried the suggestions on the error message.