iOS 14.3 email client.

You may know that there are two settings (Fetch and Push Mails). What have you set? Watch the GIF below

Google, AOL, Yahoo - Only Fetch mail Option is available

iCloud, Exchange, Outlook - Both Fetch and Push Mail option is available

1. Push Mail: Whenever possible the email client will push mails to all your devices.
2. Fetch Mail: You need to set How you want it to be fetched, Automatically, Manually , Hourly,Every 30 mins, every 15 mins
   1. Automatically: will fetch when the iPhone is powered and on WiFi
   2. Manually: with fetch when you open email, open Inbox and swipe down
   3. You get an email notification as soon as the client server receives an email and your device is connected to internet, irrespective of whether the mail is in your device's Inbox or not

The internet connectivity is the only reason for this.

Connecting to Wifi is the first part and then getting connected to the Internet is the second

1. If you connect to a Wifi, doesn't necessarily mean you are connected to the internet. If you are not connected to wifi could be a problem of iPhone settings or Router/Modem Settings
2. If you are not connected to the internet is the sole issue of Router / Modem Settings. Contact your ISP immediately

Are you using any third party apps for Gmail? Please use iOS mail app.