it helps some times You cannot pass multiple projects / arguments to dotnet publish. In your case you seem to have passed the artifacts folder as second argument. To do this, add -o before that directory:
Does that help I never came across a direct way to bring tasks for "Add Post Build Action" to "Add Build Step." Again, if I am reading your question right then you want to execute other tasks after publishing the MSTest report.
TFS 2018 Release Process - Mysterious Server Restart On "Deploy TestAgent" Build Step
This might help you According to the log, the build output is in d:\a\1\s\... the s folder it the sources directory, to access this folder there is pre-defined varaible: Build.SourcesDirectory. So instead of using $(Build.BinareisDircetory) use the above variable: