What the combination alt+enter do?

On my pc KDE Plasma sometimes freezes. System completely stops responding on mouse or keyboard, excepting cursor moving and pressing “Super” key. Picture, sound and programs continue work normally.
I randomly find Alt+Enter combination that brought my system back to normal state, what does it mean? And what could be the reason for the system freezing?
KDE 5.27.5, Kernel 6.4.2