All iPhone's drop WiFi randomly

My wife has an iPhone 12 for personal use and a XR for work. I have an iPhone 13 for personal use and a 13 mini for work. We also have an Apple TV 4K. A couple of days ago, ALL of them started to randomly drop WiFi. Since we have no cell signal and rely on WiFi calling, this means we miss calls, not to mention the inconvenience of not having internet access. Most of the time, WiFi is dropped when the phone is locked, but not always. Occasionally we lose internet access (and WiFi calling) while using the phone, yet it still shows that WiFi is connected. There were no updates on the iPhones, nor on the router. All other WiFi devices (LG TV, Onkyo A/V, Xbox Series X, and about 5 others) have solid connectivity. It only happens with the iPhones and Apple TV. In fact, the Apple TV won't even connect. I have changed no settings on my router (Archer AX6000).

I've tried the following to no avail: Forget the network and entered it again (oddly, the forgotten network still shows on our network list and it is hidden, so the phone isn't really forgetting it - I still choose Other). Broadcast the SSID. Back to hidden. Reset the network settings. Rebooted the phones. Changed SSID's and passwords to start fresh. All result in the same thing - the iPhones stop connecting randomly, and the Apple TV won't connect, despite all other non-Apple devices being fine. I am not filtering MAC addresses and no router settings have changes since everything was working.

What am I missing?