Emails show in old Outlook but not New Outlook (Mac)

Customer: *****

Customer: iMac

Customer: I have new Outlook, and can switch back and forth between old and new. But, as of 1:30 this morning, new emails fail to appear in New Outlook, but I can see them in old Outlook.

Customer: Yes. I am logged into New Outlock right now, and the latest email is yesterday. Also, other boxes such as sent and archive show nothing and indicate that things are downloading. But, when I switch to old Outlook, everything works properly.

Customer: I work on an iMac, and have use Outlook (both old and new) on it for many months. Something went screwy while I was asleep last night.

Customer: I normally use New Outlook. But when I couldn't see new emails this morning, I switched back to old Outlook and, lo and behold, the current emails were there and the other boxes were populated. In other words, old Outlook works and new Outlook doesn't (as of 1:30 this morning).

Customer: No. The New Outlook was installed when I bought the iMac a year or so ago.

Customer: I emphasize that as of yesterday (and for many months prior) New Outlook worked just fine. Something happened when I was asleep at 1:30 this morning; it wasn't something that I did.
Customer: I spent nearly two hours with AT&T/Yahoo this morning. The problem is not on their side. I can see all the emails on their web page.

Customer: Shall do.

Customer: Be patient with me.

Customer: Says that all apps are up to date

Customer: Yes

Dmytro Sywyi: Most useful advice.

Dmytro Sywyi: Let me find a different solution for you.

Dmytro Sywyi: You can restart it again if you want.

Dmytro Sywyi: Yes, but you can reconnect.

Dmytro Sywyi: Just open this page again.

Dmytro Sywyi: Good.
Dmytro Sywyi: Try to open the Outlook now.

Dmytro Sywyi: Got it.
Dmytro Sywyi: Let's try these instructions:
On the Tools menu, choose Accounts.
In the left pane of the Accounts box, select the account.
Make sure you have entered the correct email address, user name, and password.

Dmytro Sywyi: Could you send me a screenshot?

Dmytro Sywyi: Sure.

Dmytro Sywyi: Can you enter the password?

Dmytro Sywyi: Did you change it before the issue occurred?

Dmytro Sywyi: I understand.
Dmytro Sywyi: In this case, you need to log in to your Outlook again.
Dmytro Sywyi: With a new password.

Dmytro Sywyi: Please, follow the instructions below:

Customer: I have followed instruction 1, but get a screen that does not have info, two frames, or Account settiings.

On the Outlook main menu, select File > Preferences.
In the Preferences menu, select Accounts.
Click the + in the bottom left corner and select New Account.
Enter your email address and click Continue.
Enter your password.
Authenticate with Duo Mobile.
Click Done.

Dmytro Sywyi: Could you send me a screenshot?

Dmytro Sywyi: May I ask you about the version of Outlook?

Dmytro Sywyi: Good, Thank you.

Dmytro Sywyi: Please, Select Outlook > Preferences > Account. Alternatively Tools > Accounts

Dmytro Sywyi: Select your account and click on the "minus" icon.

Dmytro Sywyi: Yes.

Customer: I have created a new account.

Customer: Hey! Everything showed up! Congratulations!

Customer: Apparently, "yes".

Customer: Now, I am going to bounce back and forth from New Outlook to old Outlook. Hang in there.

Customer: And that worked. It looks like you solved the problem. Like so many things, when we finally found the solution, it was exquisitely simple.
Customer: Many thanks for your help.

Customer: And thanks for being patient with this 85-year-old man. But I used my first computer in 1958 and am pretty good at ArcGIS, Adobe Illustrator, etc., But this one buffaloed me. I needed your expertise. Thanks.