If ADR is on or off is somewhat under control of the device, though there are necessary commands from the network servver that are implicitly ADR even if ADR is nominally off.
But the fact remains that the “gateway” has zero role in it whatsoever. Gateways don’t really “do” anything in LoRaWAN other than passively transfer traffic, only devices and servers make actual decisions.
has no control on which gateway his device will connect
Devices don’t connect to gateways - they connect through gateways to network servers, and the connection has no regard for which gateway it was achieved through.
A device can only connect to the servers of the network with which it has been registered, the servers of any other network will simply ignore traffic from an unkown device reported in by their gateways.