how to add my yahoo account to Mail

I’m having the same problem. I can access my Yahoo email on my iPhone and my iPad. I can go to Yahoo.com and check it. But it is no longer accessible on my MacBook. When I try I get the same messages you are getting. Very frustrating since I work from my computer.

Much as Apple Requires an Application Specific Password when using a Non Apple e-mail Client ( Application ) to access an iCloud E-mail account

Using app-specific passwords

You may Require Logging into the Yahoo Mail Account via your Browser of choice

Us your problematic e-mail account name and password

Does it work in the Web Portal of Yahoo ?

If Yes, look for this Application Specific Password requirement on Yahoo mail

Yahoo has gone to this too...

https://help.yahoo.com/kb/access-yahoo-mail-third-party-apps-sln15241.html

Yahoo cure…

https://discussions.apple.com/thread/254879377?answerId=259375262022#259375262022

Yahoo App password…

Generate and manage third-party app passwords

Some older, third-party email apps (that do not use our Yahoo branded sign in page) require you to enter a single password for login credentials. To access your Yahoo Mail account on these apps, you'll need to generate and use an app password. An app password is a long, randomly generated code that gives a non-Yahoo app permission to access your Yahoo account. You’ll only need to provide this code once to sign in to your third-party email app.

https://help.yahoo.com/kb/access-yahoo-mail-third-party-apps-sln15241.html

Most likely biggest factor is using Other in Mail setup, then using a Browser that doesn’t have Yahoo PW stored init to get the App PW.

https://discussions.apple.com/thread/255004776

All we've ever had to do, and one account was added just last week, was to type in two bits of data: user name and password.

After that, the account was immediately active.

Before an account is added, you do have to establish the account at mail.yahoo.com per their instructions. But once that process is completed you have the user name and password to enter into the Mac mail Yahoo panels.

If your system is not allowing the above, I suggest you have something going on that's not related to the actual Yahoo email addition process.