Port forward not working on router ZTE MF286

I am trying to forward a port with my router ZTE MF286 but it is not working.

I tried several times, I restarted the router, enabled the UPnP but nothing. Any suggestion?

I tested with canyouseeme.org and other testing portal websites and the port results closed. Also, as I am trying to establish a node, I verified that no inbound connection are active.

I am using Lubuntu and I cannnot find the settings for the firewall, I understood that for most linux distribution, firewall are not active.

I imagine that my router is also a modem as it works with a sim card inside. For opening ports, you intend DMZ? I tried that also and still doesn’t work.