It's not just FB, my Samsung S9 came preloaded with 'undeletable' Microsoft apps too. But this is nothing new, Samsung phones have came preloaded with bloat since forever. When buying a new phone I always spend some time deleting all Samsung, Microsoft, Facebook and carrier related apps. Yes, you can delete 'undeletable' apps through ADB, without rooting the device. pm uninstall -k --user 0
For those of you wondering how to do it (I'm using Windows 10, but it's not that different):
1. Download Android platform tools for your platform: https://developer.android.com/studio/releases/platform-tools...
2. Unzip it, open cmd and head to the unpacked folder.
3. Enable developer tools and USB debugging in your Android.
4. List packages avaiable:
adb shell pm list packages
5. Delete the unwanted package adb shell pm uninstall --user 0 com.package.name