SharePoint Online: Remove a Field from List Content Type using PowerShell

Requirement: Remove a field from SharePoint list content type in SharePoint Online.

PowerShell to Remove a Column from List Content Type in SharePoint Online:

#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 Remove-ColumnFromListContentType()
{ 
    param
    (
        [Parameter(Mandatory=$true)] [string] $SiteURL,
        [Parameter(Mandatory=$true)] [string] $ListName,
        [Parameter(Mandatory=$true)] [string] $ContentTypeName,
        [Parameter(Mandatory=$true)] [string] $ColumnName
    )

    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)

        #Get the content type from list
        $ContentTypeColl = $List.ContentTypes
        $Ctx.Load($ContentTypeColl)
        $Ctx.ExecuteQuery()
        
        #Check if the content type exists in the list        
        $ContentType = $ContentTypeColl | Where {$_.Name -eq $ContentTypeName}
        If($ContentType -eq $Null)
        { 
            Write-host "Content Type '$ContentTypeName' doesn't exists in '$ListName'" -f Yellow
            Return 
        }

        #Get the column to delete from content type
        $ContentTypeFieldColl =  $ContentType.Fields
        $Ctx.Load($ContentTypeFieldColl)
        $Ctx.ExecuteQuery()

        $Field = $ContentTypeFieldColl | Where {$_.Title -eq $ColumnName }
        if($Field -eq $null)
        {
            Write-host "Column '$ColumnName' Doesn't exists in Content Type '$ContentTypeName'" -f Yellow
        }
        else
        {
            #Get the field link from content type
            $FieldLinkColl = $ContentType.FieldLinks
            $Ctx.Load($FieldLinkColl)
            
            #Remove field from content type
            $FieldLink = $FieldLinkColl.GetById($Field.Id)
            $FieldLink.DeleteObject()
            $ContentType.Update($false)
            $Ctx.ExecuteQuery() 

            Write-host "Column '$ColumnName' Deleted from '$ContentTypeName' Successfully!" -ForegroundColor Green 
        }
  }
    Catch {
        write-host -f Red "Error Deleting Column from Content Type!" $_.Exception.Message
    } 
}

#Set parameter values
$SiteURL="https://crescent.sharepoint.com"
$ListName="Projects"
$ContentTypeName="Project Template"
$ColumnName="Project Department" #Display Name of the Field

#Call the function
Remove-ColumnFromListContentType -SiteURL $SiteURL -ListName $ListName -ContentTypeName $ContentTypeName -ColumnName $ColumnName

When you remove a column from content type, that field become a local column in any list or library which are using that content type!