Running

qDebug() << QStandardPaths::standardLocations (QStandardPaths::ApplicationsLocation);

outputs only

("C:/Users/<USER>/AppData/Roaming/Microsoft/Windows/Start Menu/Programs")

however, this directory contains only apps relative to user.
Apps accessible to all users in Windows are located at

C:/ProgramData/Microsoft/Windows/Start Menu/Programs

, so this path must be included to returned list.