This is an stupid design of 'New Outlook', sorry for my language, the drag and drop email to 'Calendar or To Do' DOES NOT work if you have conversation mode on (which most of corporate office users have it on always in USA), you have to first turn off conversation mode, when you see individual emails then only you can drag and drop. I will ask Microsoft programmer , Why did he or she do that?
Why not just add an option on right click menu on email and call same routine as you are calling after drag and drop? This would have saved 100 of thousands of users 10 or 20 min of their productive life. If you do the math, 100,000 x 10 = 1 Million minutes = 277 hours which is 277 @ $50/hour = $13,333 or if you double it it is $26 thousand (or $50K) just gone in garbage collectively or which is average salary of United State worker.
In my view the team of programmers worked on "New Outlook' are bunch of college freshers or straight from India who have not USED Outlook on a daily basis as rest of user's community using since last tens of years. This is definitely a "QA testing" issue of Microsoft and I am seeing such negative trend with Oracle cloud products also, no real time "product usage" experience by programmer before modifying its code and bringing 'low cost' CODER straight from Market/India.
Sorry for my negative feedback but I feel it is necessary for Microsoft to read and take it seriously action.