Window too big for the screen on a Mac? How to fix it

Click the window, then on macOS Sequoia and later press Fn ⌃ F (or Window, Move & Resize, Fill). It shrinks to fit the screen exactly. On older versions, ⌥ click the green button to zoom it to fit.

Other fixes

• Drag the window up by its title bar until the bottom corner is on screen, then drag the corner to resize.
• Use another Move & Resize option, such as the left half, which always fits.
• Switch to a display setting with more space in Displays, then resize, then switch back.

Why it happens

• The app remembered a size from a bigger display.
• Some apps set a minimum size larger than a small screen.
• Plugging into a lower resolution display shrank the screen under the window.

ClutterFreeMac sizes every window to the strip, so it always fits the height of the screen. Windows that refuse to shrink past a minimum are learned, and the strip gives them the room they need instead of letting them overlap. See also an app opening at the wrong size.