Is it possible to set important schedules (construction start date, delivery date, etc.) that cannot be moved?

Yes, it is possible.

• For important schedule which cannot be changed, you can create a Bar in the Milestone Area at the top of the bar chart to fix and display it as “Milestone”.
• If you want to fix a specific activity, set “Be Fixed” in “Time Analysis Settings” of Bar Property.

Fixed date is displayed with "¤" mark which can be used as an indicator for process management.

[Fixed display of important schedule]

What is Milestone? 
It is a management point for a Project which set to the particularly important date such as delivery or deadline.
By dragging the mouse in Milestone Area, you can create a Milestone Bar.

[Fix a Bar by setting it to not move]

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