Emails deleting from folders in Outlook App

While using the Outlook for Mac app (on Macbook), I keep finding that emails are not visible in the folder I have moved them to when trying to access them later down the line.

I'm using Gmail as mail server (for work email) and can see the emails in the correct folder when accessing Gmail via web-browser but as I use Outlook as primary means of sending and receiving emails, I would prefer not to have to consult Gmail too.

Is there a way round this to stop it from happening? Any help much appreciated.

Weirdly, I can find the emails in the correct folder on Outlook App on iPhone. Just not Outlook on Macbook. Would like for all to sync as it makes for a happier life!