I want the date of attendance can't choose

At first, I chose to use columns of First Name-Last Name, Date of Attendance as keys, but there was a Virtual Column named CoputedKey.

is to want the time to open the page down when entering the event I can’t choose to enter the event because I put Today in the Initial value field and click Editable to exit.
It shows a yellow warning that The attendance date column of the timestamp table is part of the calculated key. therefore cannot be read only.