It cannot sustain the Turbo Boost speeds, therefore it throttles.
I do not know who invented the lie that CPU does not throttle if it can maintain base clock speed, but cannot maintain it's Turbo Boost speed, but that needs to stop. It is misinforming and false.
You’re severely misinformed and I cannot believe that people continue to perpetuate this nonsense. If the CPU dips below it’s advertised base clock speed then that could be construed as throttling, but needs to be divided into heat or electrically-related at that point and indicates a possible issue with either the cooling or the voltage being supplied.
If Intel meant for these CPUs to all run at their Turbo Boost frequencies, then that would have be advertised as the base frequency. But it’s not, and Intel has even built a special version of the i9 (9900KS) -
https://www.extremetech.com/computing/297858-intel-core-i9-9900ks-5ghz-all-core-boost-cascade-lake-x - that can sustain boost longer, but not indefinitely.
Intel has three different technologies in play here (emphasis mine)-
Max Turbo Frequency - Max turbo frequency is the
maximum single core frequency at which the processor is capable of operating using Intel® Turbo Boost Technology and, if present, Intel® Thermal Velocity Boost. Frequency is measured in gigahertz (GHz), or billion cycles per second.
Turbo Boost - Intel® Turbo Boost Technology dynamically increases the processor's frequency as needed by taking advantage of thermal and power headroom to
give you a burst of speed when you need it, and increased energy efficiency when you don’t.
Thermal Velocity Boost - Intel® Thermal Velocity Boost (Intel® TVB) is a feature that opportunistically and automatically increases clock frequency above single-core and multi-core Intel® Turbo Boost Technology frequencies based on how much the processor is operating below its maximum temperature and whether turbo power budget is available.
The frequency gain and duration is dependent on the workload, capabilities of the processor and the processor cooling solution.
In that ExtremeTech article they admit as much concerning Turbo Boost, “A sustained all-core 5GHz clock speed would be substantially higher than the Core i9-9900K we have here at ET —
but Intel CPU no longer hold their full clocks under sustained load. Our Core i9-9900K will turbo up to high clocks for 20-30 seconds, depending on the workload, before falling back to speeds in the lower 4GHz range when run on our Asus Z390 motherboard.”
There is nothing about sustaining Turbo Boost frequencies indefinitely and anyone trying to argue this point about
any Mac or PC is simply not dealing in reality. Intel hasn’t helped matters, with it’s marketing speak and lack of clarity about how many cores operate at what Turbo Frequency. The fact remains that any CPU maintaining it’s base frequency 24x7x365 is doing it’s job and anything extra is gravy and should not be depended on to define performance.