To enable Apple login, you need to have an Apple developer account which costs $99 per year.
1. Then you need to create an App in your Developer account.
2. Configure the certificates section of the App. See : https://prnt.sc/9Sbmcftc0s9W , make sure you enable Authorised Domains which would require an additional step.
3. Also, make sure you enable signin with Apple : https://prnt.sc/GFMRNilAok6u , you will need to enter the Auth callback url which you need to copy from firebase project.
4. Login to your firebase project, and go to Authorisation – Sign in Tab. Enable Apple and you will be see a screen to copy the oAuth url : https://prnt.sc/EetD83lrFd4c
5. Use this same URL in the App signin with Apple configuration : https://prnt.sc/hFZBnQ2dPKNC
6. Now, enable Apple as signin option in WP admin – Vibebp – Settings – General