Your situation may be a hardware failure of the phone, that is, the wifi module of the phone has a problem, which is a common fault of the iPhone. The wireless module can be replaced directly at a nearby repair outlet. You can also try rebooting and see if it works. Several solutions:
1. Settings -- General -- Cellular Mobile Network -- Cellular Mobile Data Network -- Restore Settings -- Restart.
2. Turn off the phone, connect the charger and automatically restart it, and check the WiFi repair.
3. If you use iTunes to restore the firmware, you need to back up the data in advance, right-click Device on the left of the itunes interface, and choose Transfer Purchased Product to restore the firmware.
4. Use the hot air blower to blow 1-2 cm to the right of the camera on the back for 2-3 minutes to see if the WiFi is restored.
5. Turn off the phone, wrap the whole body with plastic wrap, wrap the newspaper (do not touch the water), put the phone in the refrigerator for about 10 minutes, open the newspaper and turn it on through the plastic wrap, and check whether the WiFi is restored.