XPS 2720 Bluetooth doesn't work

Dear experts, I've some issues with my bluetooth.

System: Windows 10 Home Version: 20H2

I've tried to connect with a bluetooth device but when I try to add a new device there's always the message - connection error. Interestingly, when I use the DELL "SupportAssist" software and run "troubleshooting" & "Bluetooth port" the respective device can be found.

My interpretation: The bluetooth port generally works.

For unknown reasons it doesn't work in the "normal" mode.

What could be the reason?

Thanks for your ideas.