FancyMenu's UI Scale
FancyMenu's UI (such as the menu bar and context menus) uses a separate scale that is not linked to Minecraft's normal GUI scale.
In case FancyMenu's UI looks too small or big for you, you can change the UI scale via menu bar -> Customization -> Settings -> FancyMenu's UI.
FancyMenu 3.9.0 adds more UI scale choices. When the UI scale is set to Auto, the smallest automatic scale is now 1.25; you can still manually choose scale 1 if you prefer it.
The only exception to this are actual full screens added by FancyMenu, such as the screen to manage variables or the layout editor. These screens, in most cases, use Minecraft's normal GUI scale, but it's possible that some screens use a different auto-scaling logic to automatically show at a smaller scale when the window would otherwise be too small to fit all of the screen's content.