Is it permissible to combine the Dhuhr and Asr prayers due to being unable to perform the Asr prayer on time after work, because of a delay in returning home?

The fundamental principle is that a Muslim should prioritize obedience to Allah above all else. He should seek work that does not conflict with his acts of worship. If he cannot find such work and is compelled to take a job where he cannot perform prayer at its prescribed time, then there is no harm in combining the Asr prayer with the Dhuhr prayer, provided that this does not become a habit and is restricted to situations of need.