The word “early” is appropriate here and is to be stressed, nonetheless I am not surprised by these results, given the relative impotence of treatment effects in so many settings:

To provide causal evidence of the effects of these bans, I rely on synthetic difference-in-difference models and the National Survey of Children’s Health (NSCH) from 2016 to 2024. Currently, there are data for only one state with two post-ban periods and two states with one post-ban period, which makes the results preliminary evidence only. The outcome variables are screentime and measures of psychological wellbeing. Overall, these early results provide no clear evidence that the school ban policy reduced screentime or improved psychological wellbeing.

That is from a recent NBER working paper by Henry Saffer.