NEW YORK (NYTIMES) - When Ms Sin Yee Tsui immigrated to New York in 1982 to work as a seamstress, it took so long for her to receive letters from China that she did not learn of her father's death until after his funeral.

Everything changed after WeChat, the Chinese messaging app, was released in 2011. She now wakes up every morning to greetings from relatives, in both her old homeland and her new one, a source of cheer during her retirement in Manhattan.

"WeChat has made my life in America much happier," she said. "When I am feeling sad or troubled by anything, I no longer have to keep it all to myself."

But if WeChat - and its billion users worldwide - have created a sense of community and belonging for immigrants like Ms Tsui, the app has also exposed her to a cascade of information, disinformation and Chinese government propaganda on subjects as varied as the pandemic, Black Lives Matter and the democracy movement in Hong Kong.

Even neighbourhood news can be distorted: In August, a false post that said a beloved Chinatown bakery was closing caused a crowd to descend on the storefront. Ms Tsui's son, Justin Tsui, 37, even walked to the Manhattan bakery to prove to her that the post was wrong.

This powerful combination - the comfort and convenience of connections around the world, the isolation and distortion of an echo chamber - is common to many social media platforms.

But WeChat is unique on the American digital landscape in that it has quietly and profoundly reshaped the immigrant experience for one of the nation's fastest growing ethnic populations, the estimated five million people of Chinese descent living in America.

It has also drawn the ire of US President Donald Trump, who is trying to prohibit it.

Last Friday (Oct 2), the legal fight over WeChat's future in the United States intensified when the Trump administration appealed against a federal judge's ruling that had halted the federal government's ban of the app.

The administration has argued that WeChat endangers national security by collecting data from American users that could be retrieved by China's communist government. The federal judge in San Francisco issued a temporary injunction last month preventing the ban from taking effect, citing free speech concerns after lawyers compared it to an attempt to shut down a newspaper or television station.

The prospect of a ban, though, has rippled through Chinese-speaking communities across the country, with many like Mr Tsui and his mother expressing alarm, if also acknowledging some ambivalence.

"Even if our parents believe a little bit of this garbage on WeChat, they are still connected to their relatives, people they may never be able to see again," he said.

With 19 million regular users in the US, the app is a vital bridge to China, where almost everyone uses it and the authorities block its global competitors, including Facebook. WeChat has facilitated trade and commerce, while making it far easier for Chinese immigrants in America - students, tech workers and others - to maintain ties to friends and family.

But critics say the app has also created a Chinese-language information silo that has given Beijing's propagandists and censors a foothold in the US. Because WeChat is owned by Chinese Internet giant Tencent, keeping it under the watchful eye of the Chinese government, posts that criticise China's leader Xi Jinping or mention sensitive topics like human rights can be quickly removed, even if the authors are in the US.

The situation is of particular concern to officials who are suspicious of China's efforts to meddle in US elections, because WeChat has already helped inspire activism among a population that has long felt ignored by American politicians.

Still, for Americans to communicate with people in mainland China, there are few alternatives. WeChat is an all-in-one tool that allows users to text, share photos and videos, read news, make payments and even send virtual red envelopes of cash, a Chinese New Year tradition.

WeChat helped raise awareness about the coronavirus when it first spread in China, prompting some Chinese people in America to begin avoiding indoor dining as early as January. In New York City, Asian Americans have had the lowest virus infection rates of any racial group, the city's Department of Health and Mental Hygiene said.

During the initial surge of cases in New York, Chinese Americans quickly mobilised on WeChat to raise hundreds of thousands of dollars and ship medical supplies from China to doctors in America at a time of dire shortages.

WeChat was also filled with fearmongering rumours, including messages claiming cashiers at certain grocery stores in New York had the virus.

Mr David Wang, 50, a UPS supervisor living in Queens, is active in WeChat groups to discuss Bible passages with his friends from church, most of whom are native Chinese speakers. The online communities, which are akin to Facebook groups, form around common interests or backgrounds.

Earlier this year, one of those friends sent Mr Wang a video on WeChat, which showed bodies floating in water with Chinese captions that falsely claimed Americans were feeling so hopeless during the pandemic that they were committing mass suicide.

"We were like, where did you get this thing?" said Mr Wang, who immigrated to the US from Taiwan in 1983. "It's so absurd. We told her not to believe a lot of these things. It's bad, but it's not this crazy bad."

He has also regularly clicked on articles sent by friends, only to find the links disabled by WeChat's censors - including articles about dissidents like imprisoned Christian pastor Wang Yi.

WeChat is a vital tool for political activism by Chinese immigrants, whose political engagement and voter turnout have traditionally been low amid a lack of outreach by both major parties.

The narratives that gain the most traction on WeChat often pit Chinese Americans against other minority groups and portray Chinese people as victims of bullying and discrimination.

Right-leaning WeChat groups had a wider reach than left-leaning ones, according to a 2017 study. Many WeChat users have questioned why Mr Trump would ban a platform that is used by so many of his supporters.

Viral efforts on WeChat have also focused on elevating Chinese people regardless of political party. Last year, many groups rallied behind Democratic presidential candidate Andrew Yang, the child of Taiwanese immigrants.

Mr Phil Wong, 54, a parent and civil rights organiser in Queens, said WeChat groups helped him to galvanise thousands of Chinese parents to protest against a 2018 proposal by New York City officials to eliminate the entrance exam for admission to the city's top public high schools.

They believed the change would hurt their children's chances of getting into the schools, whose makeup is disproportionately Asian.

After the uproar from Chinese and other Asian parents, the proposal failed.

Even though WeChat has invigorated political protests by Chinese Americans, Mr Wong said he was often appalled by the anti-American propaganda on the app, including videos from the protests after Mr George Floyd's killing in May that were repackaged to amplify footage of looting and arson to promote a narrative that American democracy was evil.

"It gets me so mad," Mr Wong said. "This is not happening to every street in every city."

Prof Xing Lu, a professor emeritus in the College of Communication at DePaul University in Chicago, immigrated to the US in 1987 from China.

Early on, she often felt embarrassed at work when she was unable to understand why her American colleagues would laugh at certain jokes.

WeChat, she said, eased her sense of isolation. It became a virtual home where she and other Chinese immigrants could plan parties and share stories about their children.

She has fought in WeChat groups with friends and former classmates about their views of Mr Xi and Mr Trump. Eventually, she said, like-minded friends would form new subgroups to discuss politics, which silenced the fighting in the main group.

"We are trying to acculturate into American society, and WeChat provides this bridge for us to empower one another," Prof Lu said. "I know the US government has its own reasons to remove WeChat, but it's still a loss for the Chinese community."