Is it permissible to enter into ihram for Hajj as a Mutamatti' from Jeddah for someone coming from Egypt for work and then intending to perform Hajj, or must he return to the Miqat of the people of Egypt?

Whoever intends to perform Hajj or Umrah and is outside the Miqats, it is obligatory for him to enter into a state of ihram from the Miqat. However, for someone whose home is within the Miqat, like the people of Jeddah, he enters into a state of ihram from his home, due to the saying of the Prophet ﷺ: "And whoever is closer than that, then from where he originates." So, if you did not intend Hajj until after you arrived in Jeddah, then you enter into a state of ihram from your current location. You are not obliged to go to the Miqat, and this is what Sheikh Ibn Uthaymeen ruled for someone who was on a mission and did not resolve to perform Hajj until after passing the Miqat.