...I don't think I've heard of any sort of malware for iOS, excluding maybe very early versions. It's as solid as a rock now (even though that's the only real benefit to iOS).
Malware does exist in the modern day on iOS, but it's highly targeted and sophisticated. The most frequently mentioned is Pegasus, which is a spyware suite used to monitor certain individuals without their knowledge or consent.
Thing is, Pegasus is nowhere like the spyware most people assume it to be. For starters, it's not something that can be mass-distributed so it's not like someone can upload it to some website and trick a bunch of people into clicking a link that installs it on their device. iOS spyware is highly targeted and each malware payload has to be specifically compiled for the target device. That means if one individual device is infected, it cannot then be transmitted to another one even if it's the same model running the same iOS version. This also means that the attacker must already know something about their victim and has a very specific reason to monitor that one individual.
Another thing is that because of how complex Pegasus is and how it's only distributed by one company, it costs an attacker around $500,000 just to compile and deploy it onto a single target device. No hacker is going to fork out half a million just to infect some rando's device that probably doesn't even have anything interesting on it. iOS spyware isn't used by your average hacker who wants to steal people's bank details, it's used by certain governments to spy on various individuals for political reasons or mercenary groups to monitor their intended victims. 99.99% of people won't encounter it because they're simply not interesting enough for someone to spend $500k to spy on.
Edit: Also, a device infected with spyware generally doesn't exhibit any abnormal behaviour. Spyware is designed to stay hidden and if it alerts the user to its presence, then it kinda defeats the point of being
spyware. So when people claim their device is infected by spyware because their device is doing weird things, it shows that they clearly don't know what spyware is.