Apple recently released the fourth beta of iOS 14.5 to developers, and code suggests that updates to the platform could change in the future (via 9To5Mac).
iOS 14.5 Updates
Apple could be planning on a way to separate security updates from regular software updates. The company already does this with macOS, and iPhone and iPad users could see this happen, too.
When people using an old mac go to update, they will typically see an option for a security update and a supplemental update. Checkboxes next to each item let people control which update they want, or to install both.
Similarly, in Settings > General > Software Update, two toggles could be added for the same choice. We don’t yet know if this feature will be seen for all iPhone users, or those using older iPhones.