It sounds like you're experiencing issues with setting up your Gmail account on your iPhone 12, even though it works fine on your iPad Pro. Here are some steps you can follow to troubleshoot and hopefully resolve the issue:
Check Internet Connection: Ensure that your iPhone 12 has a stable internet connection, as this is essential for syncing mail.
Verify Gmail Settings:
- Make sure that you are using the correct username and password for your Gmail account.
- Check if two-factor authentication is enabled for your Gmail account. If so, you may need to use an app-specific password for the Mail app on your iPhone
Remove and Re-add the Gmail Account:
- Go to Settings > Mail > Accounts.
- Select your Gmail account and tap on "Delete Account."
- After deleting, re-add the Gmail account by going to Settings > Mail > Add Account > Google, and follow the on-screen instructions.
Check Mail Fetch Settings:
- Go to Settings > Mail > Accounts > Fetch New Data.
- Ensure that the settings for your Gmail account are set to fetch data regularly or are set to "Push" if available.
Update iOS:
- Make sure your iPhone 12 Pro is running the latest version of iOS. To check, go to Settings > General > Software Update.
Check Mail Sync Settings in Gmail:
- Sometimes, the sync settings in the Gmail app itself might be restricting data flow. Open the Gmail app, go to Settings, and ensure that the sync settings are set to sync all mail.
Ensure Enough Storage Space:
- Lack of sufficient storage space on your iPhone can sometimes hinder the proper functioning of apps. Check if you have enough storage space available.
Restart Your iPhone:
- Sometimes, a simple restart can resolve unexpected glitches. Turn off your iPhone and then turn it back on.
Check for Gmail Server Issues:
- Rarely, the issue might be on the server-side. You can check Google's status dashboard online to see if there are any known issues with Gmail services.