Microsoft Outlook has always had one issue or another, related to accounts and users and what not. Microsoft doesn't want people to use email accounts from other providers such as Yahoo or Google, so they make it difficult to add emails accounts to Outlook. I have had to change permissions or security options in Yahoo or Google to be able to add those accounts into Outlook.
For that reason, I tried Yahoo's email platform and I found it quick and easy to do: I added my Hotmail, Yahoo and Google email accounts pretty straightforward, they are working very well and it is pretty much the same thing. I created a shortcut on my desktop with a link to my 'Email accounts' in Yahoo and it immediately takes me to to all my email accounts without the frills of Microsoft Outlook. Microsoft always blames the user and considers us inept rookies, when some of us have been using email for longer than Microsoft's millennial engineers have been alive.
However, I kept trying to add the other accounts to Outlook and in the end it accepted Yahoo and Google accounts, by sheer randomness. I didn't follow any of the advice provided in this forum, or in Microsoft's help pages, and it started working, so I assume it's just Microsoft making it difficult for people to add accounts from other providers, but in the end they get bored of playing silly games and let users add the accounts.