Seeedstudio claims that the ICE Tower CPU Cooling Fan can reduce Raspberry Pi 4 core temperatures from 80 °C to 40 °C under load, which should eliminate thermal throttling. The ICE Tower is compatible with all previous RPi boards too and just requires 5 V power via a 40-pin GPIO. The ICE Tower is available to order now from Seeedstudio for US$19.90, which ships worldwide from July 19.
https://www.notebookcheck.net/Raspberry-Pi-Bring-the-chill-to-your-Raspberry-Pi-4-for-just-US-20-with-an-ICE-Tower-CPU-Cooling-Fan.427121.0.html