If you're looking for a cmdlet that uses that particular parameter name, try: Get-Command -ParameterName OneDriveLoopSharingCapability
However, the error you received isn't that the parameter name cannot be found, it's that the parameter is expecting a particular type of parameter value and the one you supplied isn't that.
But, looking at the help for the Set-SPOTenant cmdlet, the OneDriveLoopSharingCapability appears in the "Parameters" section, but it does NOT appear in the Syntax section. What does appear in the Syntax section is -OneDriveForGuestsEnabled.
Given the description of the -OneDriveLoopSharingCapability parameter it looks to me as if it's no longer necessary for external users you have external sharing for OneDrive for Business enabled.
You might want to bring that to the attention of the document management folks by using the "Feedback" at the bottom of the online help and explain the problem there.