Outlook window on Mac will not let me "shrink" or re-size horizontally (can't make window less wide)

Hello, I am not sure what caused this change recently, but suddenly I cannot adjust the size of my Outlook email window on my Apple MacBook Pro screen. For example, I like to have Outlook and Teams open at the same time, and usually shrink them both so they are half width and I can have them side by side. Now, I can longer make the Outlook window slimmer from the left or right. It can only stay full screen width. I can make it shorter from the bottom, still. But that is not what I want. Does anyone know why this suddenly changed, or how to fix it? I have done all the things like quit the app and reload, and restart my whole computer. Thank you.