Choose Screen Snapshot from the menu File > New or a toolbar New Generator button to generate an image of your computer screen. How it behaves depends on which operating system you use. This feature was added in Shotcut version 25.10, and it is not currently available in the Linux Flatpak (we hope to include it in the next version).
First of all, if you did not create a project folder it opens a file save dialog for you to choose the image file name and location. After the image is created, it opens in Shotcut’s Source player. From there, you can add it to Playlist or Timeline.
Windows and Linux/X11
Next, you see the following toolbar either at the top or centered on the screen:

Ironically,there is no Window button when running on Windows!
If you do not want to include Shotcut’s window, minimize Shotcut before choosing something from the toolbar. Shotcut will restore itself.
If you choose Rectangle, you need to use mouse or touch to draw a rectangle over the part of the screen to capture.
If you choose Window you need to click an application window to grab its image.
Linux/Wayland
On Wayland, there is no toolbar; it only does fullscreen capture and does not minimize Shotcut. You can edit the image (configure an Open With helper) or use a Shotcut crop video filter to isolate an area.
macOS
On macOS, there is no toolbar or fullscreen option. Rather, it goes directly into rectangle selection mode. To switch between rectangle and window selection press space before clicking anything; you will see the mouse pointer change.
Also, it always minimizes Shotcut in version 25.10. We plan to add a toolbar with an option whether to minimize Shotcut in a future version. Meanwhile, if you want to grab an image of Shotcut use shift+command+5.