Automatic insertion of the current date into a cell when entering data into an adjacent one. How to do?

Question

Google

I use the formula:
=IF(K5="sample";now();)
The date is inserted as soon as the desired text appears in cell K5. But - a problem!
If I multiply the formula by column and in cells K6, K7, ..., the necessary text appears - all dates are immediately synchronized to the current date.
How to fix so that adjacent dates remain the same?
PS
In cell K5 I have a dropdown list with several values, one of which is "sample".