Thank you but I already switched the login to Xorg.
I think though the NVIDIA GPU on this 12 year old PC might be faulty as I noticed very occasionally it would be detected on both in Xorg and Waylands logins. I tried a repo (can't remember which one) but the nvidia drivers failed to install, likely due to the Nvidia hardware disappearing during that session. Secure boot disabled or enabled didn't help with the Nvidia hardware detection or nvidia drivers install.
I did figure out a solution to getting 1440p running which was to do the following:
Log out
Select user name then click Cog icon bottom right corner to login as Xorg desktop (instead of the default which is Waylands and doesn't work with the solution below)
Open Terminal (Ctrl+Alt+T)
Use the cvt command to generate different Modelines (basically calculates and generates monitor timings) to create a new mode for the monitor in a later command. Copy (Ctrl+Shift+C) the Modeline output of this command from and including the "" onwards. Below is the values I used.
cvt -r 2560 1440 60
Note I had to use the -r flag to get it to work at all (I'd recommend trying without the -r flag first, then adding it later on if issues), likely a limitation of the monitor itself rather than the integrated Intel GPU which can output 4K. The -r flag means reduced blanking, which significantly reduces the time allocated for the horizontal and vertical blanking intervals.
Use xrandr to figure out the connected display connection name (eg "HDMI-1" which is what I will be using for the other commands below)
xrandr
TEST MODELINE FIRST
Create new display mode. Note if you create the same newmode name twice it will come up with an error bad color/font (just log out and back in to remove these temporary modes). After xrandr --newmode paste (Ctrl+Shift+V) the Modeline generated by cvt.
xrandr --newmode "2560x1440R" 241.50 2560 2608 2640 2720 1440 1443 1448 1481 +hsync -vsync
Add mode to output
xrandr --addmode HDMI-1 2560x1440R
Activate new resolution
xrandr --output HDMI-1 --mode 2560x1440R
If it fails and the screen goes black then use the cvt command to generate different values, eg add or remove -r flag, check resolution, try a different frequency eg 59.94, 50 or 30.
ONCE IT WORKS then you can permanently save the values you used, which I did as below.
nano ~/.xprofile
Copy and paste your values that worked in the xprofile (eg as below)
#!/bin/sh
xrandr --newmode "2560x1440R" 241.50 2560 2608 2640 2720 1440 1443 1448 1481 +hsync -vsync
xrandr --addmode HDMI-1 2560x1440R
xrandr --output HDMI-1 --mode 2560x1440R
Save and exit the file (In Nano: Ctrl+S then Ctrl+X).
Not sure if you need this line or not, but this just makes it so this file can be executed on login.
chmod +x ~/.xprofile
Hope that helps others in a similar situation. I did however in the end as the Intel integrated GPU wasn't powerful enough to play a 1440p video without stuttering in Xorg, went back to the Zorin default Gnome Wayland desktop and just using 1080p.
Note I also tried for many hours to enable a custom resolution in Zorin's default Gnome Wayland (as performance seemed to be faster but they maybe more to do with the higher resolution and monitor scaling set to 125% revealing the limits of the integrated Intel GPU) to add/use many different variations of a custom resolution using both an edid method and alternatively the simpler grub video= method but it didn't work for me but may work for other computers https://askubuntu.com/questions/973499/wayland-how-to-set-a-custom-resolution . The edid when it seem to trigger just went to a blank screen (so perhaps it could work for older versions of Gnome Waylands but likely a compatibility issue with new versions of Gnome Wayland so the source code may need updating or something?), and the video command seems to do something but no option ever appeared to enable 1440p in the display menu.
Note I had to remove some extra spacing from the cvt Modeline it generated for ./modeline2edid to work/calculate the Ratio 16:9 otherwise it failed to generate the source code file.