In case Gmail is not working on your iPhone properly so don't worry, In this forum, I have covered all the possible solutions to fix your problem.
- Check your Google status
- Check the Gmail website for alerts
- Check IMAP is Enabled
- Force close the mail app on your iPhone
- Restart your iPhone
- Disable iPhone Restrictions
- Update your mobile and Gmail app
See also - https://www.smartmoneymatch.com/articles/Why-has-Gmail-Stopped-Working-on-My-Phone/8724