We had the era of Slack-like interface, now it's time for Teams-like interface.
Outlook recently changed it and I absolutely hated it. Took me a good 2 weeks to get used to it. I was used to clicking on the bottom to open my calendar, now everything moved and I look everywhere BUT the left sidebar which was recently added. And, to make things worse, the icon is not your traditional calendar icon and you don't get a tooltip saying it'll open your Calendar when you hover over it.
I disliked Teams' interface for this and now I hate it even more because this seems to be the new shitty trend UX is going to.