Are the profits resulting from the aforementioned partnership work, which includes contracts from the parent company and externally, considered lawful (halal) or unlawful (haram), taking into account the contract clause that prohibits external work and the employee's ignorance of this clause when signing it?

The ruling we adhere to is that if an employer stipulates to an employee in the employment contract that the employee shall not work for anyone else, even outside working hours, and the employer has a legitimate purpose for this condition, then the employee is obligated to fulfill this condition for the employer, and it is not permissible for him to violate it. However, since you worked for the other company unaware of the aforementioned condition, there is no blame upon you. And whatever money you earned from your company, or from the other company, is lawful as long as you perform your work as required.