To get to specific proof though, clinically in the way we could with other addictions like smoking, we would need to look at how individual applications that allow us to outsource various cognitive functions specifically impact our brains.

GPS is a well studied example. Humans that rely on GPS instead of their own brains end up with provably weaker hippocampus.

https://newatlas.com/gps-spatial-direction-ucl/48529/

It is not hard to form a hypothesis from this how letting targeted content algorithms decide what you see instead of making decisions on your own could weaken the portions of your brain that make decisions in a similar way, and all studies we have seen so far seem to support this hypothesis.

I would of course like to see more brain scan research but when all data points to the negative on something only available to humans very recently, and your own lived experience of forgoing that something has had major benefits for your personally, it becomes easy to be a strong advocate for people trying out a reduction of that something.