Hi Edward,
If you want the classic look from Outlook 2016 to Outlook 2021, you need to use Outlook classic, the desktop version that comes with Microsoft 365 or with an Office edition that includes Outlook.
Here is the quickest way to get there.
First check if it is already on your PC. Open Start and type Outlook. If you see two entries, pick Outlook classic. If it opens, pin it to your taskbar. Then set it as default by opening Settings > Apps > Default apps, search for Mail, pick Outlook classic for MailTo and for the email related protocols.
If you only see one Outlook and it says new, install the desktop apps that include Outlook. Go to account.microsoft.com, sign in with the account that owns the license, choose Install Office, run the installer, then open Outlook. That will be the classic desktop Outlook with the familiar ribbon and layout.
If you do not have a license that includes Outlook desktop, the classic app is not available for free and the new Outlook will be your option.
If you want, tell me whether you have Microsoft 365 or an Office product key that includes Outlook and I will tailor the steps for your case.