Is it permissible for a person originally residing in Jeddah to enter into a state of Ihram from there, if he had gone to Riyadh for work for more than 20 days, then intended to change his workplace to Riyadh, and now wishes to return to Jeddah to collect his belongings?

If you pass a Miqat (fixed boundary for assuming Ihram) with the intention of performing a ritual, you must enter into Ihram from that Miqat, even if you are from Jeddah or Mecca. If a resident of Mecca passes by a Miqat or reaches its parallel, and intends to perform a ritual, he must enter into Ihram from that Miqat and not go beyond it. Otherwise, he will be liable for a sacrificial offering (Dam).