Open SharePoint Online Management Shell or Windows PowerShell ISE in Administrator mode.
Run the below command to install the module.
After running the above command, you will get a prompt for entering your credentials.
Click "Yes to All", when you see a message as shown below.
Once installation is completed, you will see as shown in the below screen.
Run the below Commands to get the Server Version.
Connect-PnPOnline https://mytenant.sharepoint.com
Get-PnPContext
You will see the ServerVersion (as shown below). This will be the SharePoint Online Version.
