Just to add
Same here, was wondering how motherboard itself managed to change this to such a specific value
Reporting a bug in X570 Aorus Master BIOS F5L (and likely future versions):
If you set memory multiplier to 36x or higher on the main Tweak page, the VDDG voltage will change from "Auto" to "Manual / 1.05v" in AMD CBS menu. No matter how many times you change it, it reverts. My chip is unstable with that much voltage through VDDG at my current settings, and the workaround is to keep it set to "manual" and put the correct standard VDDG voltage of 950mv.
Same here, was wondering how motherboard itself managed to change this to such a specific value