Outlook desktop client 2016/2019

If you are trying to avoid the change to the New Outlook, there are options:

If you have a paid Microsoft 365 subscription that includes "Desktop versions of ... Outlook" (not the "Microsoft 365 Business Basic" plan), you do not have to switch to the New Outlook.
https://www.slipstick.com/outlook/classic-outlook-not-new-outlook/

If you do not want to subscribe to a paid Microsoft 365 plan to get Classic Outlook, then you might want to consider buying a license for Office Home & Business 2024. This includes Outlook 2024. The latest version of the full featured, Classic, desktop, stand alone, perpetual license Outlook.

https://www.microsoft.com/en-us/microsoft-365/p/office-home-business-2024/cfq7ttc0pbm7