MAC Outlook can't change display name imap in new version

From my perspective, it appears that the root of the problem is "Microsoft Cloud". If you don't sync your email accounts with Microsoft Cloud, and instead sync directly with IMAP, you will be able to edit the first and last name of the "sender" of your email accounts. Just like we were able to do in the 90s.

Agreed, this is the issue. Clever workaround! And yet another problem in New Outlook is that it won't add an IMAP account without Microsoft Cloud unless, you specify SSL for incoming server, and, not at all obviously, StartTLS for outgoing. That's not required in Legacy Outlook; you can just specify SSL for both and call it a day, as you discovered.

So, there are two super basic problems with New Outlook (inability to change name when using Microsoft Cloud, and inability to add an IMAP account in a straightforward fashion without it).

That's right.

However, I have discovered an additional problem which is a deal-breaker for me. In New Outlook, I could not add folders to my email accounts, or Gmail accounts at the very least (the option to add folders was greyed out). In order to add a new folder, I had to revert back to Legacy Outlook. But even then, when I moved emails into a folder, most of those moved emails would not reliably appear in the folder; sometimes, some of the emails would appear when I clicked to display folder contents, but most times, a folder would only display one email, when, in fact, that folder should have been displaying about ten emails. I found this problem was only present on the desktop, and not mobile. But of course, this is a huge problem. And for that reason, I have permanently shifted to using the Mac OS and iOS Mail app. It allows me to easily edit my email accounts' sender name(s), allows me to easily set-up and reliably use folders to organize my messages, and... I am finding that it performs much faster than Outlook.
Goodbye Outlook. And, don't be surprised if I cancel my Office 365 subscription before it renews.

I mean, yes, this is correct. New Outlook, in terms of feature set and quality, is at best Public Beta status, and at this rate I don't think it will approach the functionality of Legacy Outlook for years, if ever. Literally the only thing it has going for it, in my view, is that it's snappy. I don't like any other thing about it; it's much less flexible than Legacy Outlook.

I've been advising all my clients who use Outlook for Mac to stay out of New Outlook until Legacy Outlook becomes no longer an option (and it will certainly remain an option until New Outlook offers on-premises Exchange support). Whatever its flaws, Legacy Outlook is a feature-complete and fully baked product, unlike New Outlook.

And yeah, Mac Mail is a perfectly viable and in many use cases superior alternative (and not without its own issues, but it is also a feature complete and fully baked product). It lacks some things I like in Mac Outlook like Advanced Search and Categories, but if you don't need those, I generally steer clients towards Mac Mail, with either Google, Exchange, or a specialty IMAP host behind it. (And I never steer anyone towards Outlook for iOS, even if they're using Outlook on the desktop.)

OMG THANK YOU. I was searching high and low for hours today for a fix to this, and I was just about to ditch the threads until I read this. I am beyond grateful - it's all working now.

Thanks again!

I tried everything. The only thing that worked for me was to change my profile name within contacts. Search for your email address that is populating as both email address and profile name and save it as a contact, edit change first/last name from email address to your name and save it.