Settings>Display>Navigation Bar
I would explain it but so many others have that it is probably easier if you watch this video.
I tried to find one that specifically called out the hints but after 3 videos I figured it would be easier if I tried to explain it myself. Hints replace the buttons with lines. So where there would be a button to go home or a button to go back, there is just a line. My guess is they felt it would be less intrusive, maybe look less cluttered, if instead of a button covering something a thin line was there just to show you where the button would be. Then no hints would be nothing at the bottom of the screen. You just remember where the buttons would be and swipe accordingly to navigate.
Unless there is something different about the FE variant of the S24, pressing the back button and using the back swipe gesture both work to take me back to the top of the feed in FB. Only when I'm at the top does it take me out of the app if I press the back button.
The only thing I can think to try if it is some kind of bug would be to clear the cache for your FB app. To do this;
Settings>Apps>Facebook>Storage>Clear cache.
Beyond that you might try using gestures, where you just swipe around your device with no buttons and testing if that works for you better than the buttons.
Let us know what you find.