Don't Change to the New UI.
I'm an Executive Assistant who spends most of my waking hours in the web version of Outlook 365. The old UI works. Many assistants from my team specifically use Outlook 365 on the web because the UI was/is better than the local client. The new
web UI being tested is painful to look at - I recommend keeping the old UI.
First off, Thanks for taking time to provide some feedback and for trying the new Outlook on the web experience!
I just wanted to let you know that you are able to disable two options that I think might address some of your feedback.
Click on the gear in the top right, and then disable the Sender Photos and Attachment Previews.
This will help reduce some of the colors, and reduce some of the preview pictures that are shown.
Hope this helps!