On a 28" 4K display at 3120x2160 resolution, PCGen looks awfully tiny, and the fonts are barely legible. I don't think there's a solution to improve this for Java applications from the OS side, as there is for native application, so we might need some scaling algorithm inside PCGen itself.
Opposite when running on a small tablet with 720p vertical resolution. Crowded. On a 4K display, every utility program looks tiny. Perhaps you can change your default font size or use accessibility utilities zoom it.
There is no way to scale Java applications from the outside; Java does not care for default font size sittings. PCGen should adapt its font and widget sizes to the display, both big and small.