What is a "pickup"?
Can you elaborate more on how a pickup is measured?
Question marked as
Since you provide no context I'm going to assume you mean the "pickup" counter in Screen Time.
If so, its when you pick up the iPhone and do something with it after not using it.
Just letting the screen turn on with "raise to wake", but not actually doing anything on the iPhone does not count.
It will list what apps are the most often used apps first when you pick it up after not using for a while.
More details here: Set screen time, allowances, and limits on iPhone - Apple Support