To retrieve all users in a SharePoint Online site collection using PowerShell, you can use the SharePoint Online Management Shell module. Here's a PowerShell script to accomplish this:

# Define the SharePoint Online site collection URL
$siteUrl = "https://yourtenant.sharepoint.com/sites/YourSiteCollection" # Replace with your site collection URL

# Connect to SharePoint Online
Connect-SPOService -Url "https://yourtenant-admin.sharepoint.com"

# Connect to the SharePoint site collection
Connect-PnPOnline -Url $siteUrl -UseWebLogin

# Get all users in the site collection
$users = Get-PnPTenantSite | ForEach-Object { Get-PnPTenantSiteTemplate $_.TemplateId } | Where-Object { $_.Type -eq "List" } | Get-PnPTenantList | ForEach-Object {
    $list = $_
    Get-PnPTenantUser -List $list
}

# Display user information
foreach ($user in $users) {
    Write-Host "User Display Name: $($user.DisplayName)"
    Write-Host "User Email: $($user.Email)"
    Write-Host "User Login Name: $($user.LoginName)"
    Write-Host "------------------------"
}

# Disconnect from SharePoint Online
Disconnect-PnPOnline

# Disconnect from SharePoint Online Management Shell
Disconnect-SPOService

Instructions:

In this script:

1. Define the SharePoint Online site collection URL ($siteUrl) for which you want to retrieve all users. Replace "https://yourtenant.sharepoint.com/sites/YourSiteCollection" with the actual site collection URL.
2. Connect to SharePoint Online using Connect-SPOService and authenticate with administrative credentials.
3. Connect to the specified site collection using Connect-PnPOnline and the provided URL.
4. Use Get-PnPTenantUser to retrieve all users in the site collection.
5. Display user information, such as display name, email, and login name, for each user.
6. Disconnect from SharePoint Online using Disconnect-PnPOnline and disconnect from SharePoint Online Management Shell using Disconnect-SPOService when you're done.

After updating the script with your information, save it as a .ps1 file and run it using PowerShell. This script will retrieve and display information about all users in the specified SharePoint Online site collection.