Emails are going directly to trash

I assume you are leaving your mail on the server (IMAP). In the olden days, you'd download your emails and then the mail client would delete them from the mail server (POP3). I don't think anybody has used POP3 in a long time.

Unfortunately that means that if someone or something logs into your mail account, it could be deleting them with your Apple devices never getting a vote. I could log into gmail from a friend's PC, in a browser window and delete everything in my inbox.

When I later check it from my phone, "Everything is suddenly in the trash! How did that happen?"

I'd be checking to make sure your passwords are secure and that nobody and nothing else is getting into those messages, even from other computers, old computers you forgot to log out of, etc.

Are you using any other mail apps like the Gmail app, or anything else? It could be happening anywhere.

Not a lot to go on, there...

All emails? specific emails?

From all accounts? just one account?

Do you have a rule setup to process incoming mail, and that mail is (even inadvertently) sending mails to the trash (maybe a misconfigured condition check)?