If you want to focus on one particular device and temporarily hide all the others, use Focus Mode. To put a device in focus, click the 3-dot menu button on the top-right of the device, and select Focus (hotkey F).
To exit Focus Mode, click on one of the Responsive Mode, Full Mode, or Resizable Mode icons in the toolbar, OR click the 3-dot menu, and select Exit focus.
To make it easier to switch between devices in Focus Mode, you can pin devices as tabs. To do this, click the 3-dot menu button on the top-right of the device and select Pin as a tab.
The devices you pin will be visible as tabs below the app toolbar. You can switch between devices by clicking a tab, or by using the arrow keys ⬅➡ on your keyboard.
To unpin a device, either click the ❌ button on a device tab or click the device's 3-dot menu button and select Unpin from tabs.
In addition to using the toolbar and the hotkey F, you can focus on a device using Butler.
To invoke Butler, press Ctrl+Shift+P on Windows/Linux, or Cmd+Shift+P on macOS.
In the search bar that pops up, start writing the name of the device that you want to focus on, for example, macbook. Now, select your preferred device from the list.