The Airbus a380 is an overall larger plane than the 777X). In addition to having two seating decks instead of one (the 777X has one), and four engines (777X has two) it has a larger total payload capacity than the 777X.
The max passenger capacity of the Airbus a380 is 500+ while it is only 425 for the 777X. All specific capacities are selected from what is possible, and depend on the airline’s chosen sesting configurations.
That long sleek fuselage reminds me of the Lockheed Constellation.