That's a false dichotomy.
Yes, we have agency. But it's not absolute. For instance, you don't have the agency not to use the toilet for days on end (or end up going somewhere less sanitary) if you're eating and drinking.
If you're on your third day without food, you don't have complete agency not to eat whatever food is put in front of you, even if there's some negative consequence to it. Yes, technically you can choose not to. But even if you know, without a doubt, that you will have another opportunity to get food before you would literally starve to death, there are biological and neurological processes at work that make it very, very, very hard to choose not to eat the food in front of you.
I have ADHD. In a very real sense, I am "addicted to doing engaging tasks". I don't always have full agency to choose to do a task that I know will be stressful and unrewarding. My brain treats it as if it is painful and dangerous.
Many games create a dopamine loop that is very hard to break out of. Many game companies have done neurological research to understand how to make that even stronger.
Agency is not a binary thing: you aren't either completely free of outside influence, or completely under the control of another. There are influences all around us all the time, some of which are heavy and obvious like near-starvation, others of which are much more subtle like advertising.
However much you may think you are immune to outside influences, you're not. None of us are. That's just an undeniable fact of how human brains work.