There’s a setting to open teams in the background/minimized. I’ve never seen that not work. If you want the window to open at startup as a window… then it’s working as expected, it’s not stealing focus, you told it to open at startup and above everything, zoom, steam, origin, VPN, did the same thing when I allowed them to open at startup maximized.

Not sure why you’re using the Xbox app, but I believe it also has the option to open in background.