I'm on a little older NVidia GF RTX 2070 running Zorin 18 CORE, and although it's running the 3 monitors ok, frustratingly, the one monitor is properly 2560x1440, but the other 2 monitors are limited to 1920x1080.
So... I've tried all the Drivers in the system settings, now I'm wondering if I must upgrade to Zorin 18 PRO???
Any help appreciated.
Welcome to the Forum!
No, that wouldn't change anything. Pro doesn't offer different Drivers.
Some Questions:
echo $XDG_SESSION_TYPEponce is right, pro wont change drivers
in my experience on a 2070, two of three panels stuck at 1080 is usually a bandwidth / connector thing more than zorin. dp vs hdmi, or a hub/dock that cant do three 1440p
might try forcing the mode with nvidia-settings (x11) or check if youre on wayland and the secondary outputs are getting a fallback mode. swapping which monitors are on dp vs hdmi sometimes magically lets all three do 1440
secure boot / fast startup stuff ponce asked is still worth answering first though shrug
SOLVED!
Thanks guys, you're absolutely right. It's the HDMI>DP adapters that are causing the lower resolution.
Exactly on the 2 offending monitors, once I switched the cables, I got my 2560x1440 just fine.
To answer your other questions:
Secure Boot and Fast Boot are disabled.
There never was Windows.
I'm on Wayland (that's the whole point to Zorin over Mint).
Further:
I installed ZOS CORE just to try it out, pushing for Wayland.
So far, though I don't mind spending $50 for an operating system, installing all my usual software manually (easy as pie like always), I see no reason for paying to have them installed for me.
And I'm perfectly satisfied with the display layouts offered in Core.
So I'm good here.
Thanks again for the prompt replies.
If all now working as expected, can you mark your post #4 above as 
Solution.