Hi Dennis. When I first got Outlook as part of Office 365 I had a problem with profiles. I had installed Office 365 on four Windows 10 computers, as allowed, and then found I could not start Outlook. I managed to get through to someone in support at Microsoft
(I don't remember how), and he showed me how to create a new profile and designate it as the default. I haven't had problems since, but it does require you to reinstall all your mail accounts to the new profile.
Go to the Control Panel, then search for Mail. This should bring up a link to Mail (Microsoft Outlook 2016), then click on it. This should bring up a box for mail setup with three buttons: Email Accounts, Data Files and Show Profiles. Click on Show Profiles
and see if you have a profile and have designated it as "always use". Also, use the Email Accounts button to see/add email accounts and double clicking will bring up their settings. After you designate an "always use" restart Outlook and see what accounts
are there. You may have to add them back, buts that's pretty easy except for iCloud. Use the iClould for Windows program from Apple to add the iCloud email account and other iCloud goodies to integrate with you iPhone.
If this doesn't work, I am out of ideas so try to raise Microsoft support. Good luck.