This is what happens when some new big boss appears and decides they need to shake things up to make their mark
Could "old" Outlook have used a UI refresh? Yes.
Did it need a complete rework from the ground up? No.
Was it reasonable to completely neuter features for the sake of "clean"? No.
We have the ability to switch back to "old" Outlook, but that will be taken away once Microsoft decides for us that we no longer need it.
95% of my meetings I get the initial reminder, and I set it to snooze until 5 min before the start time. I would like this to have a configurable default Snooze button action, like "old" Outlook had. No reason to remove this other than laziness and "dumbing down" the interface for the sake of aesthetics. This is a work tool, it doesn't need to be slick and pretty, it needs to be useful. Put more resources into functionality, and less into cartoonish interfaces.
Also, why can't the right sidebar show my schedule and to do list at the same time any more? Stop the ensh*ttification of Outlook >:[ Stop removing functionality for the sake of "cleanness", you're not improving the software.