Microsoft.IdentityModel.Clients.ActiveDirectory.dll was removed from MSOnline versions 1.1.183.80 and newer. So, you will get an error that this file does not exist. Use version 1.1.183.66 to resolve this issue. Install this prior to running Test-WHFB. Use the below command to install the needed version and not the most recent version.
Install-Module -Name MSOnline -RequiredVersion 1.1.183.66
Microsoft.IdentityModel.Clients.ActiveDirectory.dll was removed from MSOnline versions 1.1.183.80 and newer. So, you will get an error that this file does not exist. Use version 1.1.183.66 to resolve this issue. Install this prior to running Test-WHFB. Use the below command to install the needed version and not the most recent version.
Install-Module -Name MSOnline -RequiredVersion 1.1.183.66