MUI has no distinct button class. Instead you can make every object (even groups) behave like a button by setting an input mode for them. Several input modes area available:

None:

No input, this is not a gadget.

RelVerify:

For buttons and similar stuff.

Immediate:

Used e.g. in a radio button object.

Toggle:

For things like checkmark gadgets.

The input mode setting determines how a user action will trigger the attributes Area.Selected and Area.Pressed. See their documentation for details.