I don't recall a Bradbury story that fits your description, but it reminds me a lot of "Forgetfulness" by John W. Campbell, Jr., originally published under his "Don A. Stuart" pen name in Astounding Stories, June 1937, which is available at the Internet Archive.
Far in the future, explorers from another star visit the planet "Rhth". They find an ancient city with fantastically advanced machinery, but no inhabitants. The native Rhth men, presumably the degenerated descendants of the city builders, live in the countryside, in "twenty-foot, rounded domes":
The city flamed before him. Across ten—or was it twenty—thousand millenniums, the thought of the builders reached to this man of another race. A builder who thought and dreamed of a mighty future, marching on, on forever in the aisles of time. He must have looked from some high, wind-swept balcony of the city to a star-sprinkled sky—and seen the argosies of space: mighty treasure ships that swept back to this remembered home, coming in from the legion worlds of space, from far stars and unknown, clustered suns; Titan ships, burdened with strange cargoes of unguessed things.
And the city peopled itself before him; the skies stirred in a moment's flash. It was the day of Rhth's glory then! Mile-long ships hovered in the blue, settling, slow, slow, home from worlds they'd circled. Familiar sights, familiar sounds, greeting their men again. Flashing darts of silver that twisted through mazes of the upper air, the soft, vast music of the mighty city. The builder lived, and looked out across his dream—
But, perhaps, from his height in the looming towers he could see across the swelling ground to the low, rounded domes of his people, his far descendants seeking the friendly shelter of the shading trees—.
The Rhth men have forgotten their old technology:
"We have forgotten so much of the things the city builders knew, their arts and techniques," Seun explained. "They built things and labored that things might surround and protect them, as they thought. They labored generations that this city might be. They strove and thought and worked, and built fleets that sailed beyond the farthest star the clearest night reveals. They brought here their gains, their hard-won treasures—that they might build and make to protect these things.
"They were impermanent things, at best. How little is left of their five-million-year striving! We have no things today, nor any protecting of things. And we have forgotten the arts they developed to protect and understand these things. And with them, I am sorry, I have forgotten the thoughts that make the lathan understandable."
The Rhth men aren't dependent on the old technology; they have no use for it, get along fine without it. The visitors from space decide to colonize:
It is ordered that the first colony city on Rhth shall be established at the spot represented on the accompanying maps as N'yor, as called in the language of the Rhth people, near the point of landing of the first expedition. The near-by settlement of the Rhth people is not to be molested in any way, unless military action is forced upon the colonists.
It is ordered that if this condition shall arise, if the Rhth people object to the proposed settlement at the spot designated as N'yor, arbitration be attempted. Should this measure prove unsuccessful, military penalties shall be exacted, but only to the extent found necessary for effective action. The colonists shall aid in the moving of the settlement of the Rhth people, if the Rhth people do not desire to be near the city of the colonists.
The Rhth people are not as defenseless as they seem. The space visitors are banished from Rhth, but as a consolation, the Rhth people graciously show them where there are some other planets which they can colonize. One of the defeated would-be conquerors explains to his comrade:
"Once"—Ron Thule's voice was tense—"the city builders made atomic generators to release the energy bound in that violent twist of space called an atom. He made the sorgan to distribute its power to his clumsy shells of metal and crystal—the caves that protected him from the wild things of space.
"Seun has forgotten the atom; he thinks in terms of space. The powers of space are at his direct command. He created the crystal that brought us here from the energy of space, because it made easy a task his mind alone could have done. It was no more needful than is an adding machine. His people have no ships; they are anywhere in space they will without such things. Seun is not a decadent son of the city builders. His people never forgot the dream that built the city. But it was a dream of childhood, and his people were children then. Like a child with his broomstick horse, the mind alone was not enough for thought; the city builders, just as ourselves, needed something of a solid metal and crystal, to make their dreams tangible."
