There are multiple extensions that can keep a tab focused even if you are not looking at it.

I’ve been using “Riri Wifi et Loulou” for more than a decade. It’s a pun on the french names of Huey, Dewey and Louie (it’s supposed to be Riri Fifi et Loulou).

I second this, I have three at home, they work well.

No, I have regularly the same experience on my own Linux laptop when I want to log in to check emails on Outlook Web. It has to do with left over cookies, because from a private window it works. It’s simple incompetence from Microsoft not being able to handle this.