The claim that sexual and gender minorities are more likely to experience life dissatisfaction, isolation, and stress is true and supported by a variety of studies and credible sources. To begin, your source from the Boston University School of Public Health is reliable, as it is a top research university that receives a large amount of funding and has published thousands of peer-reviewed articles in the last year. Additionally, the author of this particular article, Jillian McKoy, is an accredited journalist and reporter, as she is a senior writer and editor at the Boston University School of Public Health. According to her LinkedIn, she has a "master's degree in public health and over 10 years of experience in journalism and public relations".
Aside from the research from your particular article being reliable, your claim can also be backed by multiple other similar studies. For example, according to an article by the Mental Health Foundation, members of the LGBTIQ+ community are more prone to mental health issues, such as depression and anxiety, due to a high experience of hate crimes, discrimination, homophobia/transphobia, social isolation, and more. Additionally, according to the US Census, "LGBT adults have consistently reported higher rates of symptoms of both anxiety and depression than non-LGBT adults", and, as shown in one of their surveys, "about 35% of non-LGBT respondents ages 18 to 29 reported symptoms of anxiety, compared with 61% of LGBT respondents in this age group".
*Although your original source does not reference the LGBTQ community and rather the SGM (sexual and gender minority populations), the LGBTQ community is included within SGM.