Is Saudia's 777-368ER The Longest Passenger Aircraft? I watched a video about passenger aircraft length (video was removed from YouTube)
It says the longest passenger aircraft is Saudia's 777-368ER.

Saudia web site says their 777-368ER is 78.86m.
But according to the Boeing web site, 777-300ER is 73.9 m.

Is the 777 be able to made longer as customer option?
I couldn't find any news souce about Saudia purchasing a modified 777.
As far as length is concerned, there are two versions of the 777 classic series, the -200 and -300. The -300 is the longer one, at 242 ft 4 in (73.86 m). Other than choosing one of these two models, there is no customer option to change the length of the plane. I'm not sure where the Saudia data comes from.

But the 777-300 is not the longest plane in the world. The A340-600 previously held that title, at 247 ft 4 in (75.36 m). The 747-8 surpassed this at 250 ft 2 in (76.3 m). The 777-9 may enter service in 2021, setting a new record of 251 ft 9 in (76.7 m).