Is there a way to increase font size in Cube Viewer?

No, sorry we don’t. We looked into it and it was very difficult to adjust the font size/scaling for all controls in a nice adjustable way. If you are using Windows 10, please look into scaling…users can keep their existing resolutions and just scale everything to look bigger. For example, take a monitor at a resolution of 3840 x 2160 (4K monitor) and scale it to 200%, it will look like another monitor which has a resolution of 1920×1080 (100% scaled).