Prime95 is NOT a reliable cpu voltage test. It is best used for testing the strength of the cpu cooler. Cinebench R23 would be better for testing Vcore.
It's hard to put the following in my own words, so refer to CompuTronix's Intel Temperature Guide:
https://forums.tomshardware.com/threads/intel-cpu-temperature-guide-2021.1488337/
As per Intel’s Datasheets, TDP and Thermal Specifications are validated “without AVX”. Prime95 with AVX test selections
enabled will impose an
unrealistic 130% workload which can
increase Core temperatures by up to 20°C. To correctly set Prime95 to run your CPU at
100% workload, simply click on the AVX test selections that are
not greyed out so that
all three AVX boxes are checked, as shown above. Further explanation concerning
AVX Instruction Sets are detailed later in this Section.
Utilities that don't
overload or
underload your processor will give you a valid thermal baseline. Here’s a comparison of utilities grouped as
thermal and
stability tests according to % of TDP, averaged across six processor Generations at stock Intel settings rounded to the nearest 5%:
Figure 11-2
Although these tests range from
70% to 130% TDP workload, Windows Task Manager interprets every test as
100% CPU Utilization, which is processor resource activity,
not %TDP workload.
Core temperatures respond directly to Power consumption (Watts), which is driven by workload. Prime95 Small FFTs
(AVX disabled) provides the correct workload for testing thermal performance. If Core temperatures don't exceed
80°C, your CPU should run the most demanding
real-world workloads without overheating.
Credit goes to CompuTronix for the guide.