People now visit the site less frequently, according to data gathered by the digital intelligence firm Similarweb. Traffic to X’s website dropped 14 percent over the past year, even as the platform still ranks with Facebook, Instagram and Snapchat as the sites and apps that Americans visit most.

X did not respond to a request for comment. In a company meeting on Thursday to celebrate the deal’s anniversary, Mr. Musk said, “We’re rapidly transforming the company from what it was, sort of Twitter 1.0, to the everything app.” He added that X had about half a billion monthly users, according to audio heard by The New York Times.

The shift has been especially felt by users who found communities on Twitter. The platform was known for its subcultures, which based their nicknames on their unifying interests: Black Twitter for pop culture, comedy and activism; Weird Twitter for unhinged joke posts; K-pop Twitter for devotees of the music genre.

Some communities have now withered. Bryan William Jones, 53, a visual neuroscience professor at the University of Utah, used to chat with other academics and pursue his hobby of photography on Twitter. He found exciting scientific research shared with the hashtag #ICanHazPDF, and used the site to organize get-togethers with other photographers.

“It’s a small world, and Twitter made it way smaller, in all the best ways,” he said.

But many of the people in Dr. Jones’s Twitter communities have left over the past year, complaining about misinformation and spam, he said. He has also scaled back his use of X, he said, after becoming annoyed by ads for items like marijuana gummies and finding that the conversations he used to enjoy had quieted down.