It looks like the Menu Font is too large for the Corkboard Options to handle. I’ve filed this as a bug.
For now the only way around it would be to use a smaller font program wide. You can do this by going to File > Options > Appearance > General Interface and choosing a smaller font size in “Menus & Windows Font”
As for “Size to fit editor”, that’s an option for adjusting the size of the index cards only, and is disabled while “Cards Across” is set to “Auto”