The Gnome Screenshot tool does that and just that, and does it well: take a screenshot. The screenshot is automatically saved to the clipboard and in "Pictures/Screenshots", so you can paste the screenshot into any editor, or open the saved file, for editing.
You are also free to use third party screenshot tools like Flameshot. Beware that Ubuntu by default now runs on Wayland. So make sure your utility of choice works well on Wayland. Alternatively, you can still switch to Xorg on Ubuntu.
You can assign the default shortcut keys, PntScr, Shift+PrtScn and Alt+PrtScn to your own screenshot tool by first disabling the default keybindings. On the "Keyboard" tab in "Settings", select "View and Customize Shortcuts". Disable the default bindings under the "Screenshot" section and create your own bindings under "Custom Shortcuts", assigning the appropriate commands for the tool you prefer to use.