Nope. When a new iOS update comes out, all supported devices may immediately install the update if they seek it out. Or it will usually auto update on its own, or at least nag the user to update.

It’s gotten slightly more confusing with the major updates now being optional. You get a choice between getting a feature update or just security patches. Unless I missed it, my phone never really asked me to update to the latest iOS 26. But I can, it’s there. I’m instead on the latest version of iOS 18. (They changed number schemes. 18 is last years major update)

Apple also does security updates for quite a long time. iOS 15, from 2021, got a security patch in September of this year, and works on the iPhone 6s from 2015.