How to force sleep in Windows 11?

In Powershell run reg add HKLM\System\CurrentControlSet\Control\Power /v PlatformAoAcOverride /t REG_DWORD /d 0 (there is no newline anywhere in this command) then restart your computer.

For more information, see this discussion on Microsoft Community.

See also a Dell community post noting that this works.

I tried this on a Dell Alienware X17 running Windows 11 Version 21H2 and it works.

Outdated information below:

Previously, it was possible to open Registry and go to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Power and set CsEnabled=0, but this hack was no longer possible after the 21H1 Windows update.