Email window keeps popping up?

I have a problem with my 2019 MacBook Air.

If I'm not currently in my mail program, but watch Netflix or YouTube, for example (mail is always open on the clipboard), then sometimes the mail program just opens and is displayed on the right half of my screen even though I don't press anything? There aren't even any new emails, it just opens like that.

Have any of you had the same problem?

Thanks in advance for all helpful answers.

(Mac OS Catalina)

Was also the case with my MacBook Pro, just quit mail completely, new mails are still displayed.

Have you already installed the latest update?

https://www.macgadget.de/News/2020/12/14/Apple-schliesst-mehr-als-50-Sicherheitsluecken-in-macOS-Mojave-und-macOS-Catalina

Again there were many bug fixes.

Has helped.