To fix the issue on my iPhone 8 Plus:
1) Open the email app and navigate back to the Inbox.
2) Simultaneously press and hold both the Home button and the Boot button (on the right side,) hold both buttons for a few seconds.
3) Simultaneously let go of both buttons. This should cause the email app to minimize and run in the background.
4) Press and hold the Boot button. Swipe right when prompted.
5) Wait a few seconds before rebooting the phone.
6) Give the phone time to reconnect to WiFi and to your cell provider.
7) Open email and see if that fixed the problem. It works for me on my iPhone 8 Plus, IOS 16.7.11.