While I agree having a secured device is important, the importance of security update has been way overblown, and there have been active scams on windows (maybe even macOS?) long before iPhone existing tricking people into installing nefarious malware disguised as security updates.On the phone?
If it's a smartphone, you typically use rich messages containing graphics, video and sound, browse the internet and read email with it.
All of which are common attack vectors (via spam or other "spray" attack method) for compromising devices. The device that you likely have Apple Pay on, do your internet banking with, have location tracking on, have 2 factor codes for work applications / banking sent to, etc. The device that has an onboard camera and microphone and knows where you are at all times.
Now, if you don't think that's worthy of keeping secure - you do you. Personally though I'd consider my phone to be just as, if not more important to keep secure than any of my other devices!
Has Apple devices been hacked to an extend fake security update is being pushed to end users? I don’t think so. Still, the weakest link of using any device is on YOU, the user, not on Apple, Google, Microsoft or others. And Apple’s opaque support policy (other than 12 month full support of the latest major version of iOS) means you either always use the latest software or take the risk of being attacked by exploits probably never going to be fixed in older versions.
I do keep all of my devices updated as much as I can, but I also don’t just update to a brand new version if there is no security benefits, for example windows 10 vs windows 11, both of which are still supported by security updates. It’s bad that Apple doesn’t have this policy (you cannot install security update of your current iOS version if there is a newer major version iOS available that your device support), but it is what it is.