Start with basic WiFi troubleshooting - as detailed here:
If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network - Apple Support
Recommended settings for Wi-Fi routers and access points - Apple Support
Consider that your Router, to which you are attempting to connect, may be configured to require support for security features that are not supported by older versions of iOS. If you have an older iPad and your router is configured for WPA3 or WPA3/WPA2 mixed authentication, you will need to change this to WPA2 PSK(AES). Newer models of iPad support WPA3.
Some Mesh WiFi Routers are known to be troublesome in some circumstances.
If you are unable to resolve the problem with your own WiFi, try setting-up your iPad from another WiFi network to which you have access - perhaps from a neighbour or friend.
Otherwise, you might be best advised to visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to offer assistance:
Genius Bar Reservation and Apple Support Options - Apple