The issue remains with macOS 12.3.1 (21E258) Monterey on Intel x86 iMac 27-inch Retina 5K display 4.2 GHz (iMac18,3; mid 2017). Magic Keyboard with Numeric Keypad & Magic Mouse 2. The issue arises only after booting. Then: Dock NOT showing - LIkewise opened applications (Command Tab) or show-hide Dock (Option Command D) or Mission Control-Exposé (F3) or LaunchPad+Dock (F4). Fixed rebooting or forcing Quit Dock (lonly process) in Activity Monitor then showing Dock and also two Dock Extra processes. Once fixed, it does not arise again until after the next boot (arises about 50% of the times). "Apple - System Preferences - Dock & Menu Bar - Dock - Automatically hide and show the dock" is selected.

Same problem here with macOS 12.2.1 (21D62) Monterey. This is a bug of Monterey. It did not happen before since Safari was released in January 7, 2003 (19 years ago). Utterly frustrating!