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ARM Cortex based ones exceed 1GHz [1]. Although, maybe the definition of microcontroller is a bit fuzzy these days.

ARM Cortex-A is an application processor, not a microcontroller. With an MMU (can run a full OS like Linux) and without internal memory.

Cortex-M is a microcontroller, without MMU (can't run Linux etc.), and typically has internal RAM and flash.

Only the NXP i.MXRT1170 reaches 1 GHz CPU clock, and this is not multi-GHz as the prior comment declared.