Donna Tartt's novels average 662 pages each.
In 2013, she explained how to keep readers engaged over such lengths.
Focus on two factors:
Density
Speed
You want the experience to move fast for the reader.
But there should still be detail.
"You want to see the quality of the shadows, the paintings on the wall, the tone of people's voice."
Don't slow down too much while showing off your fictional world.
Weave the information in as the story progresses.
Want to go deeper? There are 2 ways I can help you: