Surely all that has to happen is that users get to opt-in to these technologies.
Off by default, you actively decide.
That includes the guinea pigs at present.
You can check whether you've been press-ganged into it. The EFF has something on their site called "Am I FLoCed? A New Site to Test Google's Invasive Experiment".
You could also come up with inventive ways to make your FLoC cohort a thing of great fun and irrelevance.