So if you’re referring to the catalog, the interface docking in 2020 does take a little getting used to!
If you click & drag on the title bar of the catalog menu, it’ll let you drag it around the screen. As you drag it toward the sides, top, or bottom, a little blue rectangular icon appears there. That’s the “Docking” location. If you drop the menu there, it’ll attach itself to that side of the screen.
If you have multiple menus or catalogs docked to the same side of the screen, you might get a blue icon that looks like an NES direction pad; that will split that side of the screen with the menu you’re draggin at the bottom, top, left, or right, depending on which ‘direction’ icon you drop it on. If you drop it in the center, it’ll create a set of tabs across the bottom of that section which will let you ‘flip’ through the various menus docked on that side.