Is it permissible for an employee whose workplace is 380 km away and who returns to his family weekly to combine and shorten prayers (delaying them) when traveling to and returning from his workplace?

Your method of shortening the Isha prayer is incorrect. It is not permissible for you to shorten it in your hometown because it is your place of residence, nor in the country you travel to for work, because you will be residing there for four days or more. You must complete the prayer there. You must repeat the Isha prayers that you shortened, as your obligation for them has not been fulfilled. In the future, you must complete the Isha prayer in both locations. As for the Maghrib prayer, there is no harm in combining it with Isha as a delayed combination (Jama Takhir) if the time for Maghrib comes while you are traveling.