Hi i have the same problem, i need to disable automatic changes of the duration inserted note, dorico changes everything , it’s impossibile to composein this way.
Hi!
It would be nice to have specific examples of what you’d like to see and what you getting from Dorico at the moment!
Benji
P. S. : And welcome to the forum, Patrizia! 
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Welcome to the forum, Patrizia. If you enable Force Duration (shortcut O), you will find that Dorico notates the values exactly as you specify them.
In general we discourage this, and instead encourage you to look at the options on the Note Grouping page of Notation Options to adjust Dorico’s automatic behaviour to match your desired appearance where possible.
I understand your frustration, Patrizia. What you need to do is input your notes exactly at the orange input marker or very near it. When you click far away from the input marker then you will have the program change your note values. So remember, click right on the orange input marker to input your notes. Do not click far away from it.
Regards,
Kemar Cummings