To install this on an older device, you must download the APK from a reputable archive site, as the Google Play Store generally only serves versions for Android 6.0 and later. Instagram 109.0.0.18.124 (x86) (nodpi) (Android 4.4+)
You will be stuck with the old blue bar at the top. You won't see Notes, Broadcast Channels, or any of the AI features. It will look like Instagram from the "good old days." instagram apk android 4.4.2