Since upgrading to 16.0, when attempting to mark a Task as a Milestone, you receive an error message: “A Milestone Task cannot be Open for Time Entry.”
In this use case, you do not turn off the Time Entry feature at the Task level, but instead, it is turned off at the Project Level. If this is expected new functionality, does this mean you need to turn off the “Open for Time Entry” functionality on each task to be able to add Milestones or prevent your users from adding time to a specific task regardless if the Time Entry is turned off for the Project?
This is working as expected as part of a fix for the defect noted in: Modern UX allows milestones to be Open for Time Entry
Release : 184.108.40.2060 and above
You would need to turn off the Open for Time entry flag for each task you want to make a milestone.