XPS 8960 - Energy-Safe-Mode not available

Hello there, my XPS 8960 Desktop-PC does not support Windows "Energiesparmodus". The Machine runs hours without going into standby-mode. Dell Premium Support recommends completely reinstalling the Windows 11 Pro operating system. It is important to delete the Dell partitions. Apparently Windows has not been installed correctly. The 24/7 premium support is very difficult to reach. Answers only ever refer to the support website. Telephone contact with Dell is not possible. Do any of you have similar problems?