When the CPU is under 90-100% load, can you upload an image of TASK MANAGER to see what file or program is causing the CPU heavy usage?
By the way, The Max Operating Temperature for your Processor is 68C. This means when the temperature is reaching or has reached 68C, The Processor starts to throttle to keep the CPU temperature at or below 68C. At 71C you CPU is throttling (slowing down it speed thus reducing temperature). If it keeps going beyond 71C it will eventually shut down the computer to prevent damage to the Processor.
You have a AMD Recommended CPU Cooler for your Ryzen 1900X. You should check to make sure it is properly seated on the CPU and making good contact and is not loose where you can jiggle it a bit. Also check that the fan is running at 100% when the CPU temps are at 60C or above. That air flow is not obstructed by cable or dirty vents on the computer case or on the CPU Cooler. Make sure the fan is not being jammed or hit by a cable or wire or is misaligned in the fan case.
Leave one side of your computer case open and see if the temperature still gets very hot.
I believe, even if your CPU is under 100% load with the CPU Cooler you have installed, it shouldn't reach Max Operating temperatures at idle. That would indicate something is not working correctly with your CPU Cooler.
Possibly the Thermal Paste is not working the way it should and might need replacing.
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