After a bunch of support calls and messages with the ISP telling me this is not possible, I finally got my UniFi Cloud Gateway connected directly to the ONT WAN port successfully. Everything is working great so far.
I found the answer on random online forums. You can read whole threads in Polish here:
Łącze GPON, terminal ONT i własny router :: 4programmers.netSprawa wygląda tak: od wczoraj mam podłączony internet od INEA, jest to łącze 1000/300 w technologii…4programmers.net/Forum/Hardware_Software/372481-lacze_gpon_terminal_ont_i_wlasny_router
Konfiguracja routera dla telewizji Inea: ustawienia VLAN i połączenie z dekoderemKonfiguracja routera dla telewizji Inea ustawienia VLAN i połączenie z dekoderem. Jak ustawić router w trybie bridge, aby telewizja działała poprawnie? Doświadczenia użytkowników z konfiguracją telewizji Inea.www.elektroda.pl/rtvforum/topic3898709.html
Let there be internet
Follow this guide to get your UniFi Cloud Gateway connected to the INEA fiber optic network without using their garbage router.
Step 1. Turn off the ONT
Either press the power button on the ONT or unplug it from the wall. Leave it powered off for a few minutes.
Step 2. Get the MAC address of the ZTE INEA router
You can find the MAC address of the INEA router on the back of it. Write it down or take a photo of it.
Step 3. Modify your UniFi Network WAN settings
Plug in an ethernet cable from the ONT into the WAN port of your UniFi router.
You will need to use the MAC address of the INEA router and put it inside your UniFi Network settings.
✦IMPORTANT! Make sure to increment the last digit by 1.
In my case the last digit was 16 so I changed it to 17.
You also need to set the VLAN ID to 20, otherwise the connection will not work.
You do not need to change any other setting. Let DHCP handle the IP address.
Step 4. Power on the ONT and wait
If everything went well, your UniFi Cloud Gateway should be connected to the INEA fiber optic network and you should get a WAN IP address assigned automatically.
If it starts with 100.x.x.x then it's a CGNAT address and you need to contact the ISP to get a public IP address. But if you don't know what that means then you don't have to worry about it and your internet should work fine. You can get a public IP address by contacting INEA sales and paying an extra 10 PLN/mo as an add-on.
Orange Polska are a bunch of crooks
My new house got fiber installed. They said it was Orange who was installing it but Orange is washing their hands of it and saying it's not their network. Turns out they have an LLC called Światłowód Inwestycje which they use for laying down new fiber.
There also seems to be some sort of grace period that is rumored to last 2 years. In this period you are only able to subscribe to a plan with 1000 Mbps download and 300 Mbps upload.
All the ISPs who are leasing fiber on this network are not allowed to sell you a better package than Orange offers, despite the network supporting XGS-PON and symmetrical 10Gbps links.
Even INEA, who normally offers symmetrical fiber, cannot sell you a 1000/1000 plan because Orange blocks them from providing a better service. They are limited by the terms of Orange's Bitstream Access (BSA) contract.
They want to charge you an additional 5 PLN per month while they pretend that the network is not theirs.
Guess who's the owner of the company that installed this fiber network...
