So, here's a quick update.
I attached an external disk with Windows 11 to the Latitude and installed MS Office 2021. Then I configured Outlook with two email addresses, each with its own .pst file.
First, the good thing. The Send/Receive Buttons ON/Cancel are back!
I guess I need to reinstall Office on the main drive.


Then I sent an email to one of the two email accounts, and lo and behold, it arrived twice. Once in the inbox where it was supposed to go, and once in the other one as well.


I'll probably have to do a bit more tinkering on that this weekend.