Ask HN: How to Harden Your Phone?

Inspired by this thread - https://news.ycombinator.com/item?id=45106903

Whenever I hear the Pegasus app or read about it at HN, I get a bit worried. So, today was that day again.

I'm sure we have cybersecurity experts, security researchers, and Infosec pros here at HN. What do you recommend to keep your phone, especially an iPhone, hardened as a brick? Came across the following article, although a bit dated, which suggests not using FaceTime and iMessage. But in another search, I found iMessage is more secure than just plain old SMS/Text. I'm more worried about zero-click exploits.

https://usa.kaspersky.com/blog/how-to-protect-from-pegasus-spyware/26103/

Just a thought - would having a firewall[0] on your phone to block any incoming request or quarantine it for review will work? A response to a user-initiated request is different than an independent request coming to your phone. A clarification to avoid mixing both.

Also, a traffic monitor[1] to watch excessive outgoing traffic or excessive hard drive reads to detect if you are compromised.

I've also been thinking about developing a custom Secure Vault app, more like an isolated Sandbox; I'll share more details about it if I think I can pull it off. Any pointers, books, articles, or videos are greatly appreciated.

Security is a fascinating topic; Let's discuss.

[0] : https://apps.apple.com/us/app/guardian-firewall-vpn/id1363796315

[1]: https://apps.apple.com/us/app/traffic-monitor-with-widget/id482570191

[2]: https://www.youtube.com/watch?v=1p0Xm-Opzjg (Catching NSO Group's Pegasus spyware)

[3]: https://help.apple.com/pdf/security/en_US/apple-platform-security-guide.pdf

[4]: https://www.reuters.com/technology/cybersecurity/governments-spying-apple-google-users-through-push-notifications-us-senator-2023-12-06/