Can I use an iron remover on a ceramic-coated car?

Usually yes, provided the coating is fully cured and the iron remover is designed for automotive surfaces. Use it on a cool surface, follow the stated dwell time and never allow the product to dry. Chemical decontamination is generally less mechanically aggressive than claying, which makes it the preferred first step on coated paint. Because product chemistry varies, check whether the iron remover and the coating manufacturers recommend any limits on frequency.