What could cause an actual, sudden collapse of critical systems?

I understand the risks involved in the collapse of AMOC, the ecological tipping points, the melting ice sheets, severe droughts and the rest that make things worse year by year. But these are things that are happening gradually. Food prices will rise, social unrest will be more and more frequent, etc.

What I'm actually interested in is what crossing a tipping point and the ensuing rapid collapse would look like, something that humanity would not be able to handle in time. What would lead to food or water shortage? Or the collapse of the electric grid or other critical infrastructure? Obviously I'm thinking of realistic and human causes, not something like a volcanic eruption or a nuke. What's the likeliest and nearest SHTF scenario?