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Recommended settings for Wi-Fi routers and access points - Apple Support
If your iPhone, iPad, or iPod touch won't connect to a Wi-Fi network - Apple Support
Having cleared the basics, perhaps you have iPadOS15 WiFi Private Addressing enabled, this being enabled by default. The WiFi Private Address feature provides additional privacy and security when using “public” (untrusted) WiFi networks. This feature is largely unnecessary for your home WiFi network - and may, in some circumstances, disrupt network connectivity.
This feature is configured for each WiFi network to which you connect. As a diagnostic exercise, try disabling this feature:
Settings > WiFi > [Your Network Name / SSID] - tap the blue “i” icon - Private Wi-Fi Address - set to OFF
More information about this feature can be found here:
Use private Wi-Fi addresses on iPhone, iPad, iPod touch, and Apple Watch - Apple Support