The fourth amendment is irrelevant here. The constitution is meant to limit the power of government because government is ubiquitous and it has a monopoly on violence. If it were to become too powerful then it will oppress its citizens.

Preventing a digital platform from governing what kind of content it hosts is just absurd and makes no sense. If apple decides that it does not want to be the platform where CSAM content is distributed then they should be free to do so. If you don’t like being a part of a platform which scans images for abusive content migrate to another platform.