enlargement of iMac screen
How do I stop iMac screen from enlarging
iMac 27″, macOS 15.0
If you mean that windows on your screen enlarge sometimes when you drag a window, there are settings that you can turn off. Go to Apple menu > System Settings > Desktop & Dock and turn off "Drag windows to menu bar to fill screen" and/or "Drag windows to screen edges to tile."
Also see: Tile windows on Mac - Apple Support