Hello Tadetke
Hi, I'm Karl and will be happy to help you today.
An AT&T email account using <att.net> servers requires the use of a <Secure Mail Key> as the email account password in Outlook as described in
Create a secure mail key
https://www.att.com/support/article/email-suppo...
*** same instructions apply to any version of Outlook '2016 and later
Set up or update AT&T email - Microsoft Outlook 2016
https://www.att.com/support/article/email-suppo...
If your AT&T account uses Yahoo servers for your email account, you will need to generate a Yahoo <App Password> instead of a <Secure Mail Key>, The exact steps required to do that should be contained on your regional provider's website. My ISP also uses Yahoo servers but am not sure if the steps are the same for every provider