A new monitor might be worthwhile if your old display is no longer functioning properly due to incorrect calibration, and/or excessive brightness, contrast and sharpness settings etc.
However, your current GPU, the RTX-3070 is more than capable of rendering photorealistic shadows in Trainz when driving a properly colour-balanced display device.
Make sure you have downloaded and installed the latest nVidia drivers and have set up the monitor using their excellent nVidia Control Panel hardware-accelerated reference and colour-accuracy settings.
A good quality monitor will not require much in the way of overrides, if any, right out of the box.