Simconnect 11. missing in Global Assembly Cache

After first installation of MSFS (SU14) and SDK 0.23.1 SimConnect can’t be found in the Global Assembly Cache (GAC). Listing any SimConnect libraries yields:

C:\MSFS SDK\SimConnect SDK\lib\managed>gacutil /l | Find “simc” /i
Microsoft.FlightSimulator.SimConnect, Version=10.0.60905.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=x86
Microsoft.FlightSimulator.SimConnect, Version=10.0.61242.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=x86
Microsoft.FlightSimulator.SimConnect, Version=10.0.61259.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=x86

These are clearly from FSX-RTM, FSX-SP1 and FSX-SE.

Attempt to install it manually produces

gacutil /i Microsoft.FlightSimulator.SimConnect.dll
Microsoft (R) .NET Global Assembly Cache Utility. Version 3.5.30729.1
Copyright (c) Microsoft Corporation. Alle Rechte vorbehalten.

Fehler beim Hinzufügen der Assembly in den Cache: This assembly is built by a runtime newer than the currently loaded runtime and cannot be loaded.

It seems as if the .NET-runtime of SimConnect has a newer timestamp than the installed runtime. However, the installed runtimes are .NET Frameworks 3.5 SP1 and 4.8.1. What could be the problem here?

Best regards
-Peter