I'm currently using Edge Version 97.0.1072.21 (Official build) beta (64-bit) on Linux Mint 20.1, and I have Outlook.com installed as an Edge progressive web app. I have noticed an issue where clicking the calendar button in outlook.com will navigate to a new tab in Edge, and not display the calendar in the outlook.com PWA itself (the previous behavior). This is true for any other feature in outlook.com - People, Files, etc. Clicking any of the buttons below will just open Edge, or open a tab in an existing Edge instance:
I've got the same problem. My employer uses Outlook and I prefer Outlook.com, but out of the blue the icons changed and now when I open calendar it used to switch in the same window but it now opens in a new tab.