Paint it blue with stars to give it a celestial look.
if there’s a grate at the top paint it white to match? Is it the center you want to disguise?
It's off center but thanks.
If it’s centered in the room, cover it with a ceiling medallion. Home improvement stores carry lightweight inexpensive ones in a variety of styles.
Hang a big plant in it.
I'm not sure what part of the ceiling you're dealing with but maybe you could do something with trim and faux tin tiles? A friend of mine used both of those things to create a cool feature on their ceiling and it looks amazing!