Lost SENT MAILS on iPhone 8 after recent IOS update

After a recent IOS 16.7.7 update, my iPhone 8 had few strange disappearing SENT mails was the major one and as of yesterday it became more problematic - Gmail emails I sent via iPhone seem not to be received by any of the recipients!

Searching the internet, I think I spotted the issue: I do not have the SENT MAILBOX option for all of my Gmail accounts under Advanced>Mailbox Behaviors. However, do not have any info on how to add this SENT MAILBOX feature under Mailbox Behaviors.

As far as I am concerned this is an IOS problem since I never had this is prior to the IOS 16.7.7 update. All sent mails are not going to Gmail server and into my computer folder and also not visible on my iphone.

Anyone else have this problem?

Yes, I've tried all suggestions provided on the internet and still have the same issue. No issues with my mails on my computer.

Is there a new setting on Gmail maybe I'm missing?

Thank you.