Ambiguity with Action and Func parameter

Question

How is it possible that this code

TaskManager.RunSynchronously(fileMananager.BackupItems, package);

causes a compile error

Answer 1

Another possible explanation for this nowadays is this:

The code was written for C# version 7.3 (used by default by MSBuild 16.x, corresponding to VS2019), but the build is attempted with an earlier version of C# (which is the default for MSBuild 15.x, corresponding to VS2017).

Earlier versions of C# throw this error, but the overload is resolved correctly in C# 7.3.