Siri on wifi
For some reason, whenever I ask Siri a question when I have WiFi but not cellular turned on, she says she has connection problems. But when I turn on cellular data, she starts working again. Is Siri not available on just WiFi?
iPhone 11
It is possible for some services to work on your WiFi while others are blocked depending on the setup of your router. Also if you are using most of the bandwidth on your router streaming YouTube, etc. there will not be enough remaining for Siri to get a fast enough internet connection and she will time out.
Try restarting your router and then just use Siri, don't use anything else.