Using classic Outlook for Windows in business environments
I understand AT&T is now Yahoo and config is a bit different than the others. Keep in mind, I am a novice.
Actually, whether the account is "Yahoo" or not depends on the particular account and what servers are being used for your account which can either be <att.net> or <yahoo.com>
Depending on the version / build / channel of Outlook that you are using, you would need to use a <Secure Email Key> (if using att.net> servers) or a Yahoo <App Password> (if using Yahoo servers). You would have to check for the exact server settings for your account.
Some reference articles
Create a Secure Mail Key - AT&T Email Customer Support (att.com)
Set Up ATT Mail Settings for Microsoft Outlook 2016 - AT&T Email Customer Support
Generate and manage third-party app passwords | Yahoo Help - SLN15241
In reference to Yahoo accounts, there is also a recent change (as of Aug 2, 2023) for Outlook as it relates to the need for an <App Password> as described in
How to add a Yahoo IMAP account to Outlook Desktop without an App Password - Microsoft Support
To be clear about something, for the purposes of this, a <Yahoo Account> is considered to be any email account that uses Yahoo servers regardless of who the email service provider is. By that I mean, my ISP uses Yahoo backend servers for their email services so while the actual email address from them is a @rogers.com email address, it is a "Yahoo account"
*** I am not an AT%T customer so don't know if this would apply in any way to accounts based on <att.net> servers