What is the ruling on postponing Umrah after intending to perform it upon travelling, and in this case, does one enter into a state of Ihram from Jeddah or Ta'if?

It is not permissible to pass the Miqat without assuming Ihram for one who intends to perform Hajj or Umrah. If someone passes it and does not return, they must offer a sacrifice (dam). The Miqat for someone coming from Riyadh is Qarn al-Manazil (As-Sail al-Kabeer). If a person assumes Ihram from their Miqat, there is no blame upon them. As for one who initiates the intention for Umrah without being at the Miqat, they should assume Ihram from where they initiated the intention, whether it be Jeddah or elsewhere, based on the Prophet, peace and blessings be upon him, who said: "They are for them and for whoever comes upon them from other than them, among those who intend Hajj and Umrah. And whoever is closer than that, then from where they initiated [the intention], even the people of Makkah from Makkah."