Lenovo messed up with the X1E and P1 Gen 1 versions (and maybe later generations) in that the system boots with a thermal limit (aka Tjunction or tjmax) set to 82C (some report 80C). What this means is that regardless of power draw or under-volting settings, when your CPU hits 82C, it will drop the frequency down to the "Configurable TDP-down" frequency, or even lower. It will also may limits the system power draw.
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July 10, 2023 21:12
Fixing Thermal Throttling on Thinkpad P1 and X1 Extreme - Linux Edition