Mac calendar app no longer syncing with Yahoo calendar

Thanks for writing us @Marsus.

We understand your concern with regard to syncing of calendar. We're here to help!

Since you've confirmed that email sync works properly except for calendar, please double-check that our email server settings are correct.

If everything looks good, it would be best to get in touch with Apple support for more help. In the meantime, sign out of your email from each device, log back in, and sync your calendar to see if that works.

If you have any other questions, please feel free to write back to us.

Thank you.
David, AT&T Community Specialist.