iPhone's Magnifier, which debuted in iOS 10 to little fanfare, is a really useful Accessibility feature that few people seem to know about. It does what you'd expect - it uses the camera to magnify details that are difficult to see with the naked eye, making it perfect for reading small text or picking out other minuscule details. The original version worked by taking a snapshot of the subject which you could then zoom in on (to a much greater degree than if you just took a normal photo) and change the color of in case it would help with clarity.
Attaching metadata to your photos, like keywords, descriptions and titles, is a great way to make photos easier to find and to add further details that you might want to recall upon later viewing. If you have photos that don't come up in a natural search for their content you can just add a keyword that will ensure it is found when searched for.
iOS 14's Back Tap is an accessibility feature that literally lets you tap the back of your iPhone to access system features or start shortcut automations. For example you could assign your App Switcher to the double back tap, letting you open your App Switcher simply by tapping the back of your iPhone two or three times. There are a bunch of system and accessibility features available for Back Tap, including Control Center, Home, Screenshot, Magnifier and Zoom among others, but Flashlight is noticeably missing.
In the first major UI update since folders were introduced, iOS 14 lets you personalize your Home Screen with widgets of varying size. Obviously you can't fit every widget on your Home Screen so you have the option of adding a "Smart Stack," which is group of widgets that you can scroll through, stacked into one widget sized area. While you can remove widgets from the Smart Stack, you can't add any as it currently stands, though hopefully this will be fixed by the the time of the official release.