Is it permissible to hold Friday prayers inside a school that does not allow students to leave to perform them in the congregational mosque, knowing that there is a mosque nearby?

It is not permissible to miss Jumu'ah prayer for study or work, and you are not allowed to perform Jumu'ah prayer at school because it is not permissible to have multiple Jumu'ahs in one country without a need. You can leave work and study at this school or escalate the matter to the relevant authorities to compel the school owners to allow teachers and students to pray Jumu'ah at its appointed time in the mosque.