Is it permissible to do extra work or invest personal money in ventures that do not consume time, when the company defaults on its commitment to pay salaries monthly, given a contractual clause that prohibits working with any other entity?

The employee is obligated to fulfill the condition of not working for another party if he accepted it, based on the Prophet's (peace and blessings be upon him) saying: "Muslims are bound by their conditions." It is not permissible for him to violate this condition without the company's permission, even if the work is an investment of his private funds. As for the company's delay in paying wages, the employee has the right to demand it and all his other rights, based on the Prophet's (peace and blessings be upon him) saying: "Give the laborer his wages before his sweat dries," and "Return the trust to the one who entrusted you, and do not betray the one who betrayed you."