There is a lot of communication around modern standby (S0). As a non-native english speaker, I try to be as precise as possible. 

My 5 years old Inspiron 7590 came with modern standby. I was able to switch S0 off by 2 registry modifications and it was back to what I want = S3.

reg add HKLM\System\CurrentControlSet\Control\Power /v PlatformAoAcOverride /t REG_DWORD /d 0

reg add HKLM\System\CurrentControlSet\Control\Power /v CsEnabled /t REG_DWORD /d 0

My Precision 3590 from December 2024 came with modern standby as well and the 2 registry changes didn't help. With PlatformAoAcOverride the sleep mode disappears completely from all menus.

Your ideas are welcome how to switch S0 off.