$sb = {
    <#
    .SYNOPSIS
    Sample synopsis.
    #>    
    process { }
}
$str = [String]$sb

Set-Item -Path function:private:FunctionFromString -Value $str
(Get-Help FunctionFromString).Synopsis

Set-Item -Path function:private:FunctionFromScriptBlock -Value $sb
(Get-Help FunctionFromScriptBlock).Synopsis

> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      6.1.0
PSEdition                      Core
GitCommitId                    6.1.0
OS                             Microsoft Windows 10.0.17134
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0