i’m on vanilla openwrt don’t know about glinet gui… you should go in advanced firewall for glinet gui i guess or ssh an add interface to /etc/config/firewall add your interface to option network

config zone
        option name 'wan'
        option input 'REJECT'
        option output 'ACCEPT'
        option forward 'REJECT'
        option masq '1'
        option mtu_fix '1'
        option network 'wan wan6 wan_6 lte lte_4 wwan0'