SharePoint Lookup Field - "Add a column to show each of these additional fields"

[johndpalm]

How can I add a lookup field using PowerShell to show additional fields besides the main "ShowField" field?

I'm using Add/Set-PnpField to configure SharePoint site columns. I'm able to add a lookup column but have not found a way to add additional fields using PowerShell.

The additional field appears in the read-only property DependentLookupInternalNames but not SchemaXml.

PS> $f = Get-PnPField -Identity "FieldLookup"
PS> $f | fl -Property *

AllowMultipleValues              : False
DependentLookupInternalNames     : {FieldLookup_x003A_ID}
IsDependentLookup                : False
IsRelationship                   : False
LookupField                      : Title
LookupList                       : {d7464fe2-892b-4b7f-be5f-9624d89e6daa}
LookupWebId                      : 453e32b2-fb39-48ac-94f8-bb21901934ef  
PrimaryFieldId                   : 
RelationshipDeleteBehavior       : None
UnlimitedLengthInDocumentLibrary : False
AutoIndexed                      : False
CanBeDeleted                     : True
ClientSideComponentId            : 00000000-0000-0000-0000-000000000000  
ClientSideComponentProperties    : 
ClientValidationFormula          : 
ClientValidationMessage          : 
CustomFormatter                  : 
DefaultFormula                   : 
DefaultValue                     : 
Description                      : 
DescriptionResource              : Microsoft.SharePoint.Client.UserResource
Direction                        : none
EnforceUniqueValues              : False
EntityPropertyName               : FieldLookup
Filterable                       : True
FromBaseType                     : False
Group                            : Custom Columns
Hidden                           : False
Id                               : 4da07d23-d19e-42e8-8f61-6dbe8d755a4a
Indexed                          : False
IndexStatus                      : None
InternalName                     : FieldLookup
IsModern                         : False
JSLink                           : clienttemplates.js
NoCrawl                          : 
PinnedToFiltersPane              : False
ReadOnlyField                    : False
Required                         : False
SchemaXml                        : <Field Type="Lookup" DisplayName="FieldLookup" Required="FALSE" EnforceUniqueValues="FALSE" List="{d7464fe2-892b-4b7f-be5f-9624d89e6daa}" WebId="453e32b2-fb39-48ac-94f8-bb21901934ef"
                                   ShowField="Title" UnlimitedLengthInDocumentLibrary="FALSE" Group="Custom Columns" ID="{4da07d23-d19e-42e8-8f61-6dbe8d755a4a}" SourceID="{453e32b2-fb39-48ac-94f8-bb21901934ef}"
                                   StaticName="FieldLookup" Name="FieldLookup" Version="3" />
SchemaXmlWithResourceTokens      :
Scope                            : /teams/DevSharePointIntegrationForms
Sealed                           : False
ShowInFiltersPane                : Auto
Sortable                         : True
StaticName                       : FieldLookup
Title                            : FieldLookup
TitleResource                    : Microsoft.SharePoint.Client.UserResource
FieldTypeKind                    : Lookup
TypeAsString                     : Lookup
TypeDisplayName                  : Lookup
TypeShortDescription             : Lookup (information already on this site)
ValidationFormula                :
ValidationMessage                :
Context                          : PnP.Framework.PnPClientContext
Tag                              :
Path                             : Microsoft.SharePoint.Client.ObjectPathIdentity
ObjectVersion                    :
ServerObjectIsNull               : False
TypedObject                      : Microsoft.SharePoint.Client.FieldLookup