✔ 16.6.1 was released, use that instead.

🔥 VSTest release 16.6.0 has a major bug in Fakes in vstest.console. The 16.6.0 packages are unlisted from nuget.org, with the exception of Microsoft.NET.Test.SDK and it's dependencies which are not impacted by this problem.
Please see: #2408

See the release notes here.