New iPhone 13 - Gmail emails disappeared

Hi, I recently moved from Android to iPhone and on set up of my Gmail account the vast majority of historic mail has disappeared.

When the Mail app synced with the gmail account, there was a lot of “unread” mail which I tried to “mark all read” - I ended up deleting the app and using the Gmail app instead.

When searching for historical mail on the web browser (on laptop) the subject of the mail is found but when I click on it to open up the mail an error message “the conversation that you requested could not be loaded”.

I cannot see older messages on the app or when logged in on a browser - they appear to have disappeared and aren’t in any other folders. I tried the Google recovery tool but that did not work. Any help please?