“The market for social networks, or even what Meta is, is very different now than it was even a couple of years ago.”

The judge ruled that Google monopolized the market for two of three sets of products. It was the second time in a year that a U.S. court found it had acted illegally to remain dominant.

In her second day on the stand of a landmark antitrust trial over Meta’s power, Ms. Sandberg, the former chief operating officer, also said the company faced plenty of competition from TikTok.

The day before the visit by Jensen Huang, lawmakers in Washington said they were investigating whether the chipmaker’s sales in China violated U.S. rules.