MacBook completely frozen, spinning wheel and nothing responds

if this happens a lot rather than just once, look at free space first. a Mac with almost no storage left starts freezing all over the place. if space is fine, boot into safe mode for a while and see if it still happens, that tells you whether something you installed is causing it.

Try Command + Option + Esc first to force quit whatever's stuck. If even that does nothing, hold the power button for about 10 seconds until it shuts off. You'll lose unsaved work but nothing breaks.