airplay not working vizio smart tvs, also screen mirroring not working, spectrum said it was not their issue, mac pro trash can, mojave, will work if ethernet cable used but not wifi

I'm still working through the exact same problem as you which is how I found your question. One interesting thing is that when I used my phone as the hotspot and connected the Vizio SmartTv to the phone Wi-Fi, I found that I was able to cast everything as normal.

This led me to believe the Arris tr4400 router is the problem. Go to the URL 192.168.1.1 with the username and password being admin. I went to Wireless > Basic Setup and unchecked WMM. I went to FIrewall settings and unchecked Enable firewall and checked Enable unsolicited flow.

This now let me cast from a Google Chrome browser on my computer to the TV. However, I am still unable to cast from an iPad or a phone.