Under Display properties, you can set text to be larger than 100%, also known as Display scaling. Windows gives you 125% and 150% as standard options, but this can also be set by the user.
If display scaling is enabled, windows will automatically attempt to increase text and images to that zoom level.
However, simutrans does not behave correctly with this setting enabled, so in compatibility mode, you need to 'disable display scaling on high DPI settings'.
This setting is not necessary if display scaling is set to the default 100%.