First, please don’t listen to the advice of fellow applicants, they have no special knowledge and do not know anything you don’t know.
I have been very close to boarding schools for 20+ years, and I know there is an epidemic of mental health issues, and kids having to take leaves due to them. Which is not ideal for the kid or for the school. So the schools are trying very hard to find kids that are resilient, and don’t have any red (or yellow) flags in their application. Accordingly, I would not draw attention to it.
That said AO’s are compassionate, and realize the pandemic was difficult for so many kids, so you don’t need to make the case for them.
And it WAS tough for so many!