Psychologists and child advocates welcomed news of the landmark settlement Wednesday over claims that the social media giant Meta had harmed young users with its addictive platforms. But many expressed skepticism that the company’s planned changes would have a meaningful effect on adolescents’ mental health.

For users under 18, Meta announced it would introduce a default two-hour daily time limit, restrictions on use during nighttime and school hours and a ban on cosmetic surgery and extreme makeup filters, among other changes.

“There’s a desire to say with this kind of verdict and these kinds of changes, ‘This is going to solve the problem — this is going to protect teens’ mental health,’” said Jacqueline Nesi, an associate professor of psychiatry and human behavior at Brown University.

But research suggests that the relationship between social media use and mental health is much more complex, Dr. Nesi said. Technology can hijack young people’s time and attention, sometimes at the cost of beneficial activities like exercise, sleep or in-person interactions, and some studies have linked heavy social media use to anxiety. But the idea that social media is the primary or main driver of mental health problems in children and teenagers “is just not supported with the research,” Dr. Nesi said.

Experts agreed that the settlement and the changes Meta announced were a major symbolic victory. Sonia Livingstone, a professor of social psychology at the London School of Economics, said the measures would send “a powerful message” that platforms like Instagram are risky and should be used with care.

Candice Odgers, a professor of psychology and informatics at the University of California, Irvine, said the settlement would force Meta to design its social media platforms in a way that would make them safer — something psychologists like her have long called for.

But unless the whole industry gets on board, young people can simply migrate to other platforms, Dr. Odgers said. (On Wednesday, Meta urged TikTok and YouTube to put similar measures in place, saying that it wanted to protect teens but adding that “we cannot do it alone.”) And even there, the science remains unsettled on any causal link between social media participation and adolescent mental health, she added.

Several large-scale reviews have shown weak associations in the adolescent population between social media use and mental health, Dr. Odgers said. These have been both positive and negative. For example, she said, algorithmic feeds can harm someone who has disordered eating, but social media can be a valuable resource for people who are looking for certain kinds of information or who are in crisis.

Some researchers pointed to sleep as a potentially important factor. “We know that for many teens, the way they are using technology in general, the way they’re using social media, is getting in the way of their sleep,” Dr. Nesi said. Poor sleep over time can lead to or exacerbate anxiety and depression and can affect physical health. Teens will now be restricted from using Facebook and Instagram between midnight and 6 a.m., but “it’s an open question whether these protections will actually lead to more sleep for teens,” Dr. Nesi said. (Instagram already had an option for users to select “sleep mode” and opt out of nighttime notifications.)

In addition, six hours of sleep a night is not enough, said Catherine Steiner-Adair, a clinical psychologist and author of “The Big Disconnect: Protecting Childhood and Family Relationships in the Digital Age.”

She said the agreement for Instagram and Facebook to silence notifications during school hours also does not go far enough, because young people need relief from notifications after school hours so they can do homework or focus on other activities.

Sophia Choukas-Bradley, an associate professor of psychology at the University of Pittsburgh, said she believed the Facebook and Instagram features that would be changed are “some of the ones that have been most harmful to adolescent health.”

For example, she said, infinite scrolling and auto-playing of videos keep adolescents sucked in. “These are design features that play into and directly target adolescents’ desires to keep experiencing pleasure,” she said.

“It can feel very hard to stop checking and to stop scrolling when there might be a reward around the corner,” she said. Teens will now be able to turn off auto-play and receive prompts after 15 minutes of continuous screen time “to encourage intentional use,” Meta said in its release detailing the changes.

Dr. Choukas-Bradley said she believed disabling certain cosmetic filters would have a positive effect. She said apps that encourage adolescent girls in particular to alter their faces and bodies help them create a new ideal to which they constantly compare themselves, and that can lead to body dissatisfaction, a risk factor for anxiety and depression.

S. Bryn Austin, a professor and researcher at Harvard School of Public Health and an expert on eating disorders, said that while the settlement would give parents who use Meta’s parental supervision features the ability to select a feed that isn’t driven by algorithms as the default for their children, that would put the burden on parents, potentially creating conflict in the home while leaving children whose parents are less engaged or tech-savvy to “continue to be targeted with the algorithms.”

Jennifer Riggle, 41, a school psychologist in La Crosse, Wis., and one of the founders of a nonprofit learning collaborative called Liftoffs Learning, said she had become disturbed some years ago when she noticed how children waiting around for soccer practice to start weren’t talking to each other or even standing around daydreaming — they were on their phones.

Ms. Riggle, who is a mother of three girls ages 6 to 11, said her goal is not to raise her children to avoid technology, but to teach them how to use it wisely. While time limits are helpful, they are a “blunt measure,” she said, adding, “Two hours spent FaceTiming your grandmother or making a movie with a friend are extremely different from two hours of passive scrolling.”

Her 6-year-old has already learned to turn off Netflix right when an episode ends. “I want her to say, ‘Netflix wants me to start another show, and I’m going to say, No,’” Ms. Riggle said.