There are at least 4 possible reasons:
- Device model
- One UI Core
- Android Go
- Android versions
Device Model
Newer Samsung phones and tablets tend to have more features despite having the same Android version (One UI version). Example:
One UI Core
One UI is Samsung's customization on Android OS available since Android 9 Pie for the Samsung Galaxy series. While it packs many additional features outside of AOSP, there is also One UI Core, the stripped-down version of One UI usually found on budget models such as Galaxy M and A series.
Some known missing features:
Android Go
Android Go is an Android variant optimized for devices with low memory spec. Although not Samsung-specific, some features may be disabled:
- Notification Access
- Do not Disturb
- Picture-in-picture
- VR helper services
- Zen mode
Android versions
Android versions also affect which features are available on the device, although this is also not really Samsung-specific. (Since there are too many differences, please refer to Wikipedia for the summary of each version)
References: