If the BIOS says it supports Modern Standby, Windows takes it at its word and completely disables the ability to enter S3 sleep (classic standby). There’s no official or documented option for disabling Modern Standby through Windows, which is incredibly annoying.
Side note: for a while, there was actually a registry setting you could change to disable Modern Standby on the Windows side. Unfortunately, Microsoft removed it, and to my knowledge, has never added it back.
I'm not a Windows user, so I can't confirm one way or the other, but toward the end of the end of the article the author gives vendor-specific instructions for disabling the S0 Low Power Idle capability from BIOS.