Stop Duplicate Cells

can I prevent duplicate entries in a column

Of course, you can do it.

Select a sufficiently large range in the right column (for example A2:A500).

Apply a conditional formatting to the selected range:

  1. With the formula

    COUNTIF($[First cell]:[Current cell];[Current cell])>1

2. With special condition “duplicated values”

(IMHO, this conditional formatting not will be saved in the final document - when you open the table you will need to redefine it)