Is there a way to increase the font size in this game? I can't even get through the 1st mission without my eyes needing a break.

I experienced the same issue and I solved it in lowering the resolution of the game to 1280 x 1024, it still looks good and is more confortable to play.

4k UHD Specific Solution & Issues

By default, Earth 2160 will attempt to set the maximum width of the HUD to 1024. This can be altered by changing the value of MaxInterfaceWidth, found in HKEY_CURRENT_USER\Software\Reality Pump\Earth2160\Interface. For an optimized HUD size, divide the current resolution's width by 2, and set MaxInterfaceWidth to the result. For example, for a monitor resolution of 3840x2160, divide 3840 by 2 to get 1920.

so fill in 1920 where before was 1024(decimal)

Some custom hud settings can be found here based on your game resolution here: https://github.com/InsideEarth2160/Files/tree/main/Misc