In order for a Button from Figma to be imported to Unity automatically, certain rules apply when designing a button in Figma.
A button component set in Figma
Unity Importer Plugin
In order for Figma Importer to understand which component it is trying to convert a figma node to a Unity UI element, Component Type from Unity Importer plugin must be selected as desired component type. "Button" component type should be selected when designing a button.
"State" variant
Buttons have 4 states: Default, Hover, Press, Disabled. These states must be designed as variants of a button component in Figma.
The hierarchy of child nodes of a component set's variant must be the same for each and every one of them.
Keep in mind that components & component sets are never imported to Unity, only instances of them are imported.