Copy list items from multiple source lists to a single target list

I have been given a task to make a script in CSOM. I am very new to Powershell so any help would be appreciated.

I have a site collection with multiple calendars within the sites. I have to create a script that will look for new events in multiple calendars and copy the events to a single target calendar. I can copy from a source calendar to a target calendar but cannot seem to get multiple calendars sources.

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"

Function Copy-ListItems()
{
    param
    (
        [Parameter(Mandatory=$true)] [string] $SiteURL,
        [Parameter(Mandatory=$true)] [string] $SourceListName,
        [Parameter(Mandatory=$true)] [string] $TargetListName
    )   
    Try {
        #Setup Credentials to connect
        $Cred = Get-Credential
        $Cred = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.UserName,$Cred.Password)

        #Setup the context
        $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
        $Ctx.Credentials = $Cred

        #Get the Source List and Target Lists
        $SourceList = $Ctx.Web.Lists.GetByTitle($SourceListName)
        $TargetList = $Ctx.Web.Lists.GetByTitle($TargetListName)

        #Get All Items from Source List
        $SourceListItems = $SourceList.GetItems([Microsoft.SharePoint.Client.CamlQuery]::CreateAllItemsQuery())
        $Ctx.Load($SourceListItems)
        $Ctx.ExecuteQuery()

        #Get each column value from source list and add them to target
        ForEach($SourceItem in $SourceListItems)
        {
            $NewItem =New-Object Microsoft.SharePoint.Client.ListItemCreationInformation
            $ListItem = $TargetList.AddItem($NewItem)

            #Map each field from source list to target list - INTERNAL NAMES
            $ListItem["Title"] = $SourceItem["Title"]
            $ListItem["Location"] = $SourceItem["Location"]
            $ListItem["EventDate"] = $SourceItem["EventDate"]
            $ListItem["EndDate"] = $SourceItem["EndDate"]
            $ListItem["Description"] = $SourceItem["Description"]
            $ListItem["Category"] = $SourceItem["Category"]
            $ListItem["RecurrenceData"] = $SourceItem["RecurrenceData"]
            $ListItem["fRecurrence"] = $SourceItem["fRecurrence"]
            $ListItem["TimeZone"] = $SourceItem["TimeZone"]
            $ListItem["XMLTZone"] = $SourceItem["XMLTZone"]
            $ListItem["UID"] = $SourceItem["UID"]
            $ListItem["Duration"] = $SourceItem["Duration"]
            $ListItem["EventType"] = $SourceItem["EventType"]
            $ListItem.update()
        }
        $Ctx.ExecuteQuery()

        write-host  -f Green "Total List Items Copied from '$SourceListName' to '$TargetListName' : $($SourceListItems.count)"
    }
    Catch {
        write-host -f Red "Error Copying List Items!" $_.Exception.Message
    }
}

#Set Parameters
$SiteURL= "https://site.sharepoint.com/teams/site/"
$SourceListName="Test Calendar"
$TargetListName="Destination Calendar"

#Call the function to copy list items
Copy-ListItems -siteURL $SiteURL -SourceListName $SourceListName -TargetListName $TargetListName

Credit to: https://www.sharepointdiary.com/2017/01/sharepoint-online-copy-list-items-to-another-list-using-powershell.html

I have to copy from multiple sources and skip if duplicate.

Thank you in advance.