That's because the daily mission is actually part of the season pass, which you have to pay extra for. The season pass for season 1 (and hence, season 5 which just finished) was included for free with the WONY expansion, but all other seasons require additional purchases.
Unfortunately, this means that, unless you buy the season passes, you'll never be able to get rid of that 'new projects available' marker except by going into the UI editor and hiding that box. It's an annoying bug, but has been reported plenty of times before.