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If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network - Apple Support
Internet connection difficulties are usually an indication that your device does not have a routable IP Address - your IP Address usually being assigned by DHCP. When this occurs, your iPad may only have a self-assigned link-local IP address that begins 169.254.x.x.
If you have a VPN App or profiles installed, or a security App such as Norton, these may be interfering with DHCP and preventing your device from obtaining a valid IP Address for your iPhone hotspot - or the WiFi network to which you are attempting to connect. The resolution is usually simple; if installed, you may only need to temporarily disable or remove the Security App and/or VPN.
DHCP is frequently used to automatically obtain an IP Address. Until your iPad has a valid IP Address to connect to your network, you will not have an internet connection. Disabling or removing VPN and/or the offending security App should allow DHCP to operate normally - allowing connection to your network and the internet.
If this resolves your issue, the VPN and/or security App can be reinstated after the connectivity problem has been resolved.
Be aware that Hidden WiFi networks offer absolutely no security benefit whatsoever - as hidden WiFi networks are trivial to discover using commonly available software tools. Hidden SSIDs engender a false sense of security - and contrary to expectations, actually exposes you to network spoofing attacks that are designed to compromise your WiFi network password. Unless you understand the associated risk - and have a pressing reason to use this feature - you would be well advised to cease using this facility.
Recommended settings for Wi-Fi routers and access points - Apple Support