Do you know if actual child abuse also proliferated?
Your comment unfortunately exemplifies the problem of tech people trying to define the problem away rather than directly address the harms involved or propose privacy-respecting technical solutions to proactively mitigate it.
As far as I know, we don't have official numbers (at least not shared as part of the discussion). But what we know is, those scanners have a significantly high error rate and will overwhelm law enforcement with false-positives. What we also know is that law enforcement is simply not competent enough, there was a case in Germany where they just removed links in a Forum forgetting to sweep the according link targets to file hosters.