Still report as well, it sends emails to the mods and the admins. Just make sure it’s identifiable at a glance, like just type “CSAM” or whatever 1-2 words makes sense. You can add details after to explain but it needs to be obvious at a glance, and also mods/admins can send those to a special priority inbox to address it as fast as possible. Having those reports show up directly in Lemmy makes it quicker to action or do bulk actions when there’s a lot of spam.
It’s also good to report it directly into the Lemmy admin chat on Matrix as well afterwards, because in case of CSAM, everyone wants to delete it from their instance ASAP in case it takes time for the originating instance to delete it.