One of the ways social media can be beneficial to mental health is in finding community (at least if it is a healthy one, and not toxic like in the last section). For example, if you are bullied at school (and by classmates on some social media platform), you might find a different online community online that supports you. Or take the example of Professor Casey Fiesler finding a community that shared her interests (see also her article):
I think the people have forgotten what social media was created for - a means to connect people around the world. Forgetting this core idea is probably what has made social media so harmful as now it is used for almost every aspect of our life except the simplicity of connecting with someone.