Key doesn't exist:

which versions are you using
SonarQube: 9.1.0 Community
SonarScanner for MSBuild:

we changed from the developer edition to community edition of SonarQube. Since the version shift a jenkins ms-build failed with the error:

Key doesn't exist: This property should be set by the plugin in SonarQube.

We don’t find this specific key in SonarQube and or neither in the plugin. How to fix this key error?

That analyzer id relates to the Security SonarAnalyzer C#, which is supported in Developer edition but not in Community edition. My guess is that you have a Quality Profile that is still referencing rules from the Security SonarAnalyzer C# repository. Is that the case, and if so what happens if you deactivate them?

A SonarQube update to a newer version resolved the problem. The rules were updated and the C# rules were dropped.