Add-Type -Path (Resolve-Path "C:Program FilesCommon Filesmicrosoft sharedWeb Server Extensions16ISAPIMicrosoft.SharePoint.Client.dll")
Add-Type -Path (Resolve-Path "C:Program FilesCommon Filesmicrosoft sharedWeb Server Extensions16ISAPIMicrosoft.SharePoint.Client.Runtime.dll")

Function Get-SPOContext([string]$Url,[string]$UserName,$Password)
{
    write-host Get-SPOContext
    $Context = New-Object Microsoft.SharePoint.Client.ClientContext($Url)
    $Context.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($UserName, $Password) #SecurePassword
    return $Context
}

$UserName = "lee@xxx.onmicrosoft.com"
$Password = Read-Host -Prompt "Enter password" -AsSecureString
$Url = "https://xxx.sharepoint.com/sites/Developer"
$listTitle="MyList"
$FieldName="Comment"

$Context = Get-SPOContext -Url $Url -UserName $UserName -Password $Password
$List = $Context.Web.Lists.GetByTitle($ListTitle)
$Context.Load($List)
$Context.ExecuteQuery()

#Retrieve field
$field = $List.Fields.GetByInternalNameOrTitle($FieldName)
$Context.Load($field)
$Context.ExecuteQuery()
$field.SetShowInEditForm($false)
$field.UpdateAndPushChanges($true)

$Context.ExecuteQuery()

write-host Done