In case this trips up anyone else, I found that in the FLT file, you cannot set the MissionType in the Main section to anything you want anymore, as of recently. I had my Osprey-specific mission Mission Type set to “Osprey Missions” and that used to create a new category under Activities / Custom Content, but in the most recent version of MSFS the mission or category does not appear at all. I had to change MissionType to “FreeFlight” and it appears now.