SharePoint Online: Export-Import Site Columns using PowerShell

Requirement: Export-Import Site Columns in SharePoint Online.

SharePoint Online: Export Site Columns using PowerShell
This Powershell script exports all site columns of a specific group fro SharePoint Online site to a XML file.

#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"

#Function to export site columns from a group
Function Export-SPOSiteColumns([String]$SiteURL, [String]$SiteColumnGroup,[String]$XMLFile)
{
    Try{
        #Setup the context
        $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
        $Ctx.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.Username, $Cred.Password)
    
        #Get All Site Columns of the Web
        $Ctx.Load($Ctx.Web)
        $Ctx.Load($Ctx.Web.Fields)
        $Ctx.ExecuteQuery()

        #Get the site column Group
        $SiteColumns = $Ctx.Web.Fields | where {$_.Group -eq $SiteColumnGroup}
        if($SiteColumns -ne $NULL)
        {
            #Wrap Field Schema XML inside <Fields> Element 
            Add-Content $XMLFile "`n<Fields>"

            #Loop through each site column of the group
            ForEach($Field in $SiteColumns)
            {
                Add-Content $XMLFile $Field.SchemaXml
            }
            #Closing Wrapper
            Add-Content $XMLFile "</Fields>"

            Write-host -f Green "Site Columns Exported Successfully!"
        }
        else
        {
            Write-host -f Yellow "Could not find the Site Column Group '$($SiteColumnGroup)' at '$($SiteURL)'"
        }
    }
    Catch {
    write-host -f Red "Error Exporting Site Columns!" $_.Exception.Message
    }
}

#Set Config Parameters
$SiteURL="https://crescent.sharepoint.com"
$SiteColumnGroup="Crescent Projects"
$XMLFile="C:\Temp\CrescentSiteColumns.xml"

#Get Credentials to connect
$Cred= Get-Credential

#Call the function to export the Site Column group to XML
Export-SPOSiteColumns $SiteURL $SiteColumnGroup $XMLFile

Once executed, this PowerShell script exports all site columns from the given site column group to a XML file as below:

Import Site Columns from the XML File 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"

#Function to Import site columns from a XML file
Function Import-SPOSiteColumns([String]$SiteURL, [String]$XMLFile)
{
    Try{
        #Setup the context
        $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
        $Ctx.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.Username, $Cred.Password)
    
        #Get XML file contents
        [xml]$FieldsXML = Get-Content($XMLFile)

        #Remove the "Version" Attribute from the XML
        $FieldsXML.Fields.Field.RemoveAttribute("Version")

        #Loop Through Each Field
        ForEach($Field in $FieldsXML.Fields.Field)
        {
            #Check if the web has the field already!
            $Ctx.Load($Ctx.Web.Fields)
            $Ctx.ExecuteQuery()

            $SiteColumn = $Ctx.Web.Fields | Where {$_.InternalName -eq $Field.Name}
            If($SiteColumn -eq $Null)
            {
                #Add Site column to Web
                $SiteColumn = $Ctx.Web.Fields.AddFieldAsXml($Field.OuterXml, $True,[Microsoft.SharePoint.Client.AddFieldOptions]::AddFieldToDefaultView)
                $Ctx.ExecuteQuery()
                Write-host "Site Column Added:" $($Field.Name)
            }
            Else
            {
                Write-host -f Yellow "Site Column '$($Field.Name)' Already Exists!"
            }
        }
        Write-host -f Green "Site Columns Imported Successfully!"
    }
    Catch {
    write-host -f Red "Error Importing Site Columns!" $_.Exception.Message
    }
}

#Set Config Parameters
$SiteURL="https://crescent.sharepoint.com/sites/marketing"
$XMLFile="C:\Temp\CrescentSiteColumns.xml"

#Get Credentials to connect
$Cred= Get-Credential

#Call the function to Import the Site Columns from XML
Import-SPOSiteColumns $SiteURL $XMLFile 

Here is my another post on exporting and importing site columns in SharePoint On-premises using PowerShell: How to Export-Import Site Columns in SharePoint using PowerShell?