Include calendar for public holidays
Chris Maljanovski commented
In local/traditional calendars you can easily spot which days are public holidays and Sundays, because they are marked with the color red. By "public holidays and sundays" I explicitly mean non-working days. in Sweden for example, Christmas Eve is a holiday, but it's STILL a working day. I consistently go to other calendar apps just to see which days are non-working days, and would appreciate it A LOT if this was possible in Outlook as well.
Add the holidays. You know you can do it. It's ridiculous not to have them.