You have a power limit throttling problem. This has nothing to do with your CPU cooler or airflow.
The default turbo power limits for a 10850K are not enough to achieve maximum performance during a stress test. At default settings, during any long term test, the CPU will be forced to slow down so it does not exceed the 125W rated TDP.
If your cooling is adequate, you might need 250W or a little more to maintain maximum performance and zero power limit throttling during a stress test. I like running Cinebench R20 or R23 which is a realistic full load test. Some people like running Prime95 but I think that is an excessive load compared to the apps and games that most people run.
Have a look in your BIOS for the long and short term turbo power limits which are also called PL1 and PL2.
Increase PL1 from 125W to 250W or beyond. If you cannot find this setting in your BIOS, you can use ThrottleStop or the bloated Intel XTU to access the turbo power limits in real time.
I set my 10850K to 300W for PL1 and PL2. No more power limit throttling except when doing some extreme overclocking. No need to use the Lock option unless your computer is changing the power limits while in Windows.
Most 10850K are programmed to use excessive voltage at default settings. A -50 mV undervolt is usually 100% stable and can help reduce full load power consumption and temperatures significantly. Here is an example of a 10850K running a full load Cinebench test reliably at under 60°C. Reducing the voltage can really help.
Use HWiNFO to see what it reports for VCore voltage when the CPU is loaded. Ignore the XTU VID voltage value.