Can you censor anyone from posting CSAM on Nostr? No.
Can you censor anyone from making a inscription CSAM on Bitcoin? No.
Why is SimpleX even worried about what some no-life pedos do on a self-hosted private group chat?
It's a battle you can't win, and is far too often used as an excuse/trojan horse to censor other things, push for anti-privacy and encryption backdoors. Look at the UK mess recently.