You don't have to assume your user wants to be A/B tracked, or wants to purchase anything. You can allow the user to enable them nicely and non-intrusively without a popup. You can ask the user intrusively when they actually initiate a purchasing action.
Most sites choose do popup instead because (they think) it is more effective. So be it, but don't say it's "mandatory" or that "they are forced to".
Crazy how people whose job it is to build this crap, don't even know what the actual rules are.
It's almost as if they just want to collect all the data on all the users forever without any oversight, by continuously rehashing bad and misunderstood versions of the GDPR and pretending it's hard and complex and vague.