High contrast for Calendar
The colors on the calendar are far too pastel/faint and ruin the point of categorizing the events. In addition, All Day Events need to retain the "background" color by category, for the same reason.
New UI stil lacks a high-contrast setting like the O365 'Teams' section has.
Accessibility for people with visual impairments in current and new Ouitlook UI is terrible due to the lack of sufficient contrast in the design.
'Dark mode' is useless for this purpose as it reduces contrast even more.
The contrast on the calendar colours is very low. Much prefer the visibility of the old style but don't think that that's perfect either.