The original claim that 99% of high school/ college students say misinformation in news increases their anxiety is slightly misleading. The source claims that 99% of their survey respondents (3272 high school + college students) claimed that they believe misinformation is a problem with our news today, however, only 82% claim that world news has a negative impact on their mental health. Nowhere in the primary data does NSHSS claim that 99% of students say misinformation directly increase anxiety for them.
With that said, it's also important to keep in mind that this survey only represents a very slim group of the country's youth, and a vague group at that given that there is no demographic data beyond age and graduation year. In addition, the survey is admittedly quite informal, as there is no mention anywhere on their website or slideshow about the methods and controls that the researchers at NSHSS used to conduct this survey, which means for all we know, respondents could have been presented with survey questions in a misleading fashion.
In essence, given the informality of the survey research conducted by NSHSS, and the slight inaccuracy of the claim, I would say that this initial claim is no where near definitive.
Links to NSHSS's website and data:
https://www.nshss.org/resources/teen-trends-survey-2025/
https://www.nshss.org/media/iwwdrktq/nshss-2025-teen-trends-survey-final.pdf