There are tons of proposed explanations. Starting with "during covid, boys were less isolated due to them socializing via computer games way more then girls". Continuing through "different body standards and societal expectations" (tho those did not changed in covid). In addition, some mental illnesses are simply genetically more prevalent in one gender then in the other.

Those are all speculations tho.

Historically, also issues like alcoholism, anorexia, drug use had different rates between genders. It is not unprecedented for one gender to be affected differently then the other.