Yesterday I found an app that I need to keep my bluetooth headphone from entering sleep mode. It is Sound Keeper: https://veg.by/en/projects/soundkeeper/. And it uses exactly the same approach talked in this article. For example, normally its filename is SoundKeeper64.exe. But if you rename it to SoundKeeper64AllOpenOnly.exe, it switches behavior to operate on "All" devices with the "OpenOnly" mode.