As described, the restriction that suggests the presence of a management profile - that in turn implies that the device is centrally managed by an Enterprise or Educational establishment.
Devices that are configuration locked by an MDM platform can usually only be released from central management by the platform that manages the device. Be aware that Apple will not assist with removal of management profiles.
Unless you are lucky - and have the option to delete the profile from iPad Settings - you’ll need to seek assistance directly from the System Administrator who manages the device. Otherwise, the device is useless.
Install or remove configuration profiles on iPad - Apple Support