Can I use transformations to anonymize data for client-side destinations?

You can use transformations to delete a property before it's sent to a client-side destination, but we don't support a way to anonymize client-side events. This is because destinations loaded client-side will already have access to a user's IP address, at which point it is no longer possible to truly anonymize that user.

If you want to anonymize a user, you should use ID Masking with the destination configured in server-side mode.