For grouped Table and Gallery views, select this icon from your database view. 

Choose 'Hide' to hide this group from the view.

Repeat for any additional views you want to hide, including 'Empty' groups.

You can then toggle on or off whether these 'Hidden groups' are expanded or remain hidden in this view!
Click here.

You can then toggle on or off whether these 'Hidden groups' are expanded or remain hidden in this view!

For Kanban board views, you'll find your Hidden groups by scrolling all the way to the right of your board.

Hide/Show Hidden Groups In Notion