Found the solution to this problem:
Since even reinstalling Windows 11 and updating all drivers did not help, I thought that TurboActivate might have problems with virtual network cards and Windows traditionally has a lot of them.
With the command in the Power Shell (the normal Cmd is not enough here!):
Get-WmiObject -Class “Win32_NetworkAdapter” | Format-List -Property Name,PhysicalAdapter,MacAddress
all network adapters are listed. If a false is displayed for the “PhysicalAdapter” parameter or the adapter does not show a “MacAddress”, then it is virtual.
On my system, there were several Microsoft miniports and a Microsoft debug adapter, as well as a virtual Wifi adapter. You can display these in the Windows Device Manager, but first select that you also want to see hidden devices (can be found under View). Simply uninstall the devices and start Reefmaster - it worked perfectly.