Is the salary received by a manager considered permissible if he does not fully perform his job duties, but rather spends his time browsing the internet under the pretext of giving employees freedom of action?

Work is a great trust that must be performed as required and agreed upon. Negligence in it is a betrayal of trust and a dereliction of responsibility. It is not permissible to leave the workers under your responsibility to their consciences and to be distracted from them by the internet. You must fear Allah regarding what you have been entrusted with. If you are unable to carry out the task of supervising the work and holding negligent individuals accountable, then excuse yourself from this work and seek another that you can fully perform.