The problem with Gmail not loading new emails on your iPhone can be quite frustrating. However, the good news is that this problem is actually very simple to fix. The first thing you need to do is to make sure that IMAP is enabled in your GMAIL account. This is a must-have feature for all email accounts. If you're not sure how to do this, you'll need to follow these steps.
Check also - https://apfashiontech.com/how-to-solve-gmail-not-working-issues/