Expand record : impossible to view multiple tasks with different dates in one expand record


I have many projects with several tasks over several days. I can regroup by project and put my tasks on different lines, to be able to assign a specific date to them. Except that when I do that I no longer have the possibility to expand record and see all my tasks for the project. If I group all the tasks on a single line, I can see them when I expand record but I can no longer assign specific dates to the tasks!
If you have a solution thank you for your help!

I can send pictures to understand if necessary