Samsung rolled out the Night Mode for the Galaxy Note9 back in June, but at the time it was only for the German units. Well now, the company has expanded this feature to the US as well.
A new update (with version N960USQU2CSGA) is seeding for Verizon's Note9 which brings Night Mode to the device in addition to the July 1, 2019 security patch.
Samsung has released an update for the unlocked units as well, but it doesn't include the Night Mode.
It's also unclear when exactly the Galaxy Note9 units on other carriers will get the Night Mode.
Got it on my unlocked N960F. Yes it is rolling out globally on S9 & S9+ too: Samsung Galaxy S9 and S9+ get Night Mode in new update (SAGAR, 11 JUNE 2019): https://m.gsmarena.com/samsung_galaxy_s9_s9_plus_june_2019_security_patch-news-3751...
From the camera settings ,reset to default and then the night mode will apear.