SharePoint Online: Fix "The collection has not been initialized. It has not been requested or the request has not been executed. It may need to be explicitly requested" Error in PowerShell

Error: The collection has not been initialized. It has not been requested or the request has not been executed. It may need to be explicitly requested.

Root cause:
You must load the object before you are trying to retrieve its properties!

Solution: Here is how the problem can be resolved

#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"
  
#Parameters
$SiteURL = "https://crescenttech.sharepoint.com"
$UserName = "[email protected]"
$Password = "Password goes here"
$SecurePassword= $Password | ConvertTo-SecureString -AsPlainText -Force
 
#Setup the Context
$Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
$Ctx.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($UserName, $SecurePassword)
 
#Get All Fields from the List
$List = $Ctx.Web.Lists.GetByTitle("Documents")

#Load List Fields collection
$Ctx.Load($List.Fields)
$Ctx.ExecuteQuery()

ForEach($Field in $List.Fields)
{
    Write-host $Field.Title
}

Please note, if you skip the Line # 19 and 20, you would end up with the error The collection has not been initialized!
Let's taken another example to retrieve all list names from a SharePoint Online site:

Import-Module Microsoft.Online.SharePoint.PowerShell -DisableNameChecking

#Parameters
$SiteURL = "https://crescent.sharepoint.com/sites/Projects"
 
#Setup Credentials to connect
$Cred = Get-Credential

#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 List names from the site
$Lists = $Ctx.web.Lists
ForEach($List in $Lists)
{
    Write-host $List.Title
}

The above script fails with an error message:

The collection has not been initialized. It has not been requested or the request has not been executed. It may need to be explicitly requested. At C:\Users\Salaudeen\Documents\PowerShell\Get-Lists.ps1:15 char:9 + ForEach($List in $Lists) + ~~~~~ + CategoryInfo : OperationStopped: (:) [], CollectionNotInitializedException + FullyQualifiedErrorId : Microsoft.SharePoint.Client.CollectionNotInitializedException

Here, in this case, we should load the Lists collection first. So, to fix the issue, use:

Import-Module Microsoft.Online.SharePoint.PowerShell -DisableNameChecking

#Parameters
$SiteURL = "https://crescent.sharepoint.com/sites/Projects"
 
#Setup Credentials to connect
$Cred = Get-Credential

#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 List names from the site
$Lists = $Ctx.web.Lists
$Ctx.Load($Lists)
$Ctx.ExecuteQuery()

ForEach($List in $Lists)
{
    Write-host $List.Title
}

So, make sure collection objects are loaded and executed before accessing them inside loop!