Why does my phone keep disconnecting from my wi-fi

Please check --> Recommended settings for Wi-Fi routers and access points ...

Is this linked to a specific event? Mine seems to be doing it during FaceTime phone calls and not during regular phone calls. I have gone through thorough support with Apple and they claim it’s a new feature for iOS 13 and that it is working as intended. I have turned off WiFi assist and changed networks, reset network settings, gotten a new SIM card, router replacement, so on, and so on.