CheckSPVersion.ps1

# Change to your URL
$Site = "https://tenant.sharepoint.com"

# Code

#Add references to SharePoint client assemblies and authenticate to Office 365 site
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"

#Obtain username and password
$Username = Read-Host -Prompt "Please enter your username"
$Password = Read-Host -Prompt "Please enter your password" -AsSecureString

#Connect to root Site Collection and obtain version

$Context = New-Object Microsoft.SharePoint.Client.ClientContext($Site)
$Creds = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Username,$Password)
$Context.Credentials = $Creds
$Context.ExecuteQuery()

Write-Host "Server Version:" $Context.ServerVersion -ForegroundColor yellow