What are you calling the "lowest level"? Because at the CPU level there is no arbitrary scope mutex. That's not a thing that exists at the lowest levels. The mutex/lock that exists in basically every language is actually built on top of atomics, that's your "building block" so to speak.

There is an x86 instruction prefix named 'lock', but it only applies to a single instruction and is considered in the family of being atomic rather than a mutex.