Deactivated phone won’t work

When I got a new iPhone, I intended to let my son use my old iphone11 on our home WiFi. It says it connects to WiFi with no issue, but no apps works. It says it cannot establish a secure connection and will sometimes add that it cannot verify server identity.

There are no issues with the WiFi itself.

The phone connected to this WiFi daily when it was activated. It was still working perfectly when I upgraded.

I’ve tried it on other home WiFis with the same results.

Resetting the network settings did not help. How do I get the phone to work?