As far as I know there’re no GUI option to turn off NAT on WireGuard connection. We have to manually edit /etc/config/wireguard to add “option masq ‘0’”. See the example below:
config peers 'wg_peer_XXX'
option name 'XXXX'
option private_key '....'
option end_point 'XXX.XXX.XXX.XXX:XXXX'
option public_key '...'
option allowed_ips '...'
option masq '0'