Isn’t connmand used by default? So don’t change /etc/resolv.conf
but connmand’ s nameserver config. First list the services:
# connmanctl services
*AO SSID wifi_xyz_xyz_managed_psk
*A XYZ cellular_IMSI_context123
Next you can change the nameserver:
# connmanctl config wifi_xyz_xyz_managed_psk --nameservers 9.9.9.9
That change should apply to AD as well but will be overwritten by every network change.