SharePoint Online: Add Calculated Column to List using PowerShell

#Load SharePoint CSOM Assemblies
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.dll"
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.Runtime.dll"
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.Taxonomy.dll"

#Custom function to add column to list
Function Add-CalculatedColumnToList()
{ 
    param
    (
        [Parameter(Mandatory=$true)] [string] $SiteURL,
        [Parameter(Mandatory=$true)] [string] $ListName,
        [Parameter(Mandatory=$true)] [string] $Name,
        [Parameter(Mandatory=$true)] [string] $DisplayName,
        [Parameter(Mandatory=$false)] [string] $Description=[string]::Empty,
        [Parameter(Mandatory=$true)] [string] $FieldsReferenced,
        [Parameter(Mandatory=$true)] [string] $Formula,
        [Parameter(Mandatory=$true)] [string] $ResultType
    )

    #Generate new GUID for Field ID
    $FieldID = New-Guid

    Try {
        $Cred= Get-Credential
        $Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.Username, $Cred.Password)

        #Setup the context
        $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
        $Ctx.Credentials = $Credentials
        
        #Get the List
        $List = $Ctx.Web.Lists.GetByTitle($ListName)
        $Ctx.Load($List)
        $Ctx.ExecuteQuery()

        #Check if the column exists in list already
        $Fields = $List.Fields
        $Ctx.Load($Fields)
        $Ctx.executeQuery()
        $NewField = $Fields | where { ($_.Internalname -eq $Name) -or ($_.Title -eq $DisplayName) }
        if($NewField -ne $NULL)  
        {
            Write-host "Column $Name already exists in the List!" -f Yellow
        }
        else
        {
            #Frame FieldRef Field
            $FieldRefXML=[string]::Empty
            $FieldRefs = $FieldsReferenced.Split(",")
            foreach ($Ref in $FieldRefs)
            {
                $FieldRefXML = $FieldRefXML + "<FieldRef Name='$Ref' />"
            }

            #Create Column in the list
            $FieldSchema = "<Field Type='Calculated' ID='{$FieldID}' DisplayName='$DisplayName' Name='$Name' Description='$Description' ResultType='$ResultType' ReadOnly='TRUE'><Formula>$Formula</Formula><FieldRefs>$FieldRefXML</FieldRefs></Field>"
            $FieldSchema
            $NewField = $List.Fields.AddFieldAsXml($FieldSchema,$True,[Microsoft.SharePoint.Client.AddFieldOptions]::AddFieldInternalNameHint)
            $Ctx.ExecuteQuery()    
            
            Write-host "New Column Added to the List Successfully!" -ForegroundColor Green  
        }
    }
    Catch {
        write-host -f Red "Error Adding Column to List!" $_.Exception.Message
    }
} 

#Set parameter values
$SiteURL="https://crescent.sharepoint.com"
$ListName="Projects"
$Name="TotalInvestmentBuffer"
$DisplayName="Total Investment Buffer"
$Description="5 Percentage in Total Investment"
$Formula = "=([Total Investment]*5)/100"
$ResultType="Currency" 
$FieldsReferenced="[Total Investment]" #Fields Names participating in Formula. Should be Comma (,) Separated

#Call the function to add column to list
Add-CalculatedColumnToList -SiteURL $SiteURL -ListName $ListName -Name $Name -DisplayName $DisplayName -Description $Description -Formula $Formula -ResultType $ResultType -FieldsReferenced $FieldsReferenced

#Parameter
$SiteURL = "https://crescent.sharepoint.com/sites/pmo"
$ListName= "Projects"
 
#Connect to PnP Online
Connect-PnPOnline -Url $SiteURL -Interactive

#Add a calculated column to list
Add-PnPField -List $ListName -Type Calculated -InternalName "Buffer" -DisplayName "Buffer" -Formula "=[Budget]*0.10"