Now conjecturing as to correlation confounders. Maybe the girls need more time at home with pets, family, hobbies, more time in their yard, less time exposed to commuting and classes they don't want to take or people they don't want to see. School is such a diverse set of stressors and the data here isn't clear to begin with...
A more verified takeaway is that girls attempted suicide around 2X more often than boys. This we know has something to do with technology and social media, whereas the schools opening is still potentially spuriously linked.