Ubuntu is not Manjaro - so it maybe due to something ubuntu-specific tweaking.
I don’t know anything on screen sizes bigger the normal FHD but if your graphics support it then Manjaro support it - suffice you installed the necesary driver.
If you are not able to apply a supported resolution you should look at the driver setup.
Run the nvidia configuration utility and setup your monitor(s) - save the settings locally and apply then globally - then reboot to activate them.