Links don’t open. “404 not found”

Some websites, or all websites?

Reboot, and try again.

Reboot your router, and try again.

Any VPN client or ad-blocker or content filter apps installed? If so, disable or remove those, and try again.

(404 is the HTTP page not found status, so you are connecting to a webserver, which usually means DNS is working.)

Change you DNS settings to use a different (and potentially more reliable) DNS Service than the automatic settings you iPad might currently be using.

This can either be set on a per-device basis in Settings, or can be set-up on your home Router. I strongly recommend using one of the following services - for which IPv4 and IPv6 server addresses are listed:

Quad9 (recommended)

9.9.9.9

149.112.112.112

2620:fe::fe

2620:fe::9

OpenDNS

208.67.222.222

208.67.220.220

2620:0:ccc::2

2620:0:ccd::2

Cloudflare+APNIC

1.1.1.1

1.0.0.1

2606:4700:4700::1111

2606:4700:4700::1001