Is it permissible to take additional quantities of food, drinks, and fruits from the company restaurant's buffet designated for employees, given that the company managing the restaurant does not object to it?

Regarding eating more than necessary from an open buffet, it depends on the verbal or customary permission of the owner of the meals. If permission is granted, there is no harm. Otherwise, it is forbidden, because the Prophet, peace and blessings be upon him, said: "The property of a Muslim person is not lawful except with his willing consent."