Why does my system reboot during big battles in Expeditions: Rome?

I felt absolute despair when my PC black-screened during peak action in Rome, killing my immersion. I tried disabling CPU Turbo Boost in BIOS, but that was a disaster; it reduced reboots but crashed my frame rate from 90 to 55 FPS. I finally used the GamePP Power Plan Switcher to activate High Performance mode and set the motherboard load-line voltage to medium. After testing, the 12V rail stabilized at 11.9-12.1V per HWInfo64, with final stability confirmed at 12.0-12.1V via AIDA64, while fans hit 1100-1300 RPM per SpeedFan. It's a lifesaver to finally save