In Kemet WordPress Block Theme, we care about every aspect of design elements, so we've amended Button Block with new options to help you to create buttons that you're looking for. By default WordPress 5.9 comes with two default styles Fill and Outline.
Rounded Button in Kemet Full Site Editing Theme
In Kemet Theme, you can create a rounded button by navigating to Button Block Settings > Styles > select Rounded.
Button Shadow in Kemet WordPress Block Theme
In Kemet Theme, you can create Button with Shadow effect by navigating to Button Block Settings > Styles > select With Shadow.