Configuration Rasberry pi 3 b+ with Huawei b310s-22 modem

Hello i want to set a firewall in the raspberry, until now I tried to config the internet in the raspberry following this guide:

So I understand that I need to set a a WAN interface looking at the eth0, but in the tutorial they are using a PPPoE, I would like to know if there is another option, in the modem I can get Dinamic IP and also I can set a static IP, but triying to fit them into Lucy did not ended good. Can someone confirm me if this router is the problem? iam going to ask to the operator anyway, i had never heard of a PPPoE username or password but there are on the options in the modem

you have one RJ45 LAN/WAN Gigabit why not connect the RPi using it ?

and no, RPi port doesn't have to be WAN.

RPI is connected with ethernet cable and making an access point, but it is not getting internet, in fact it is throwing my internet connection on the wifi network when i set it up.

I think i got what u mean, it is about the network config I saw in this other guide, althoug it might oudated since it doesnt bring me internet conection too

Alright, after looking in the instructions in the page I found that it is needed to configure the DNS and the gateway on the LAN in the access point. But I realice that the problem could be the modem since it is a sim modem it get into eternet mode and thats why i think I lost the internet conection

If the PI have a static IP set on the port, you manually have to specify the DNSes too.

I got configure it to get internet wifi to the RPI and then to the desktop pc thought the cable, so it is at least working