Standing is obligatory only for Takbeer Tahreema in Fardh salah (Obligatory Prayers) with which the prayer begins. After that a person can sit. This is the opinion of imam Shafaee and others.
People should not take their Shāfiʿī fiqh from the previous paragraph. Rather, the ruling is that individuals who are able to stand must do so in obligatory prayers. Individuals who cannot stand can pray sitting, lying on their side, or lying on their back. One is not required to stand in non-obligatory prayers, though the reward is halved. Some of this was mentioned in an earlier Evident Conspectus article. Here is the relevant passage from The Evident Memorandum, from the section on integrals of prayer:
2. Standing in obligatory prayers, when one is capable of doing so. If one is unable to stand, he does whatever his situation allows. Someone able to stand may perform voluntary prayers sitting, lying on his side (but not by nodding), and lying on his back.
Due to him ﷺ saying to ʿUmrān ibn Ḥuṣain, “Pray while standing. If you cannot, then pray sitting. And if you cannot, then pray lying on your side.” Al-Bukhāri transmitted it. Al-Nasāʾī’s adds: “And if you are not able, then on your back: ‘Allah does not burden anyone with something save what is within their ability,’ [Q2:286].’” [Bukhāri (1117); Nasāʾī (1660)]
Concerning nodding, there is a ḥadīth in al-Dāraquṭnī with a chain that cannot be cited as proof. [Dāraquṭnī (1320, 4713)]
As for the rest of the article: I have seen chairs in every mosque I have ever prayed at in the Middle East. Even in the mosque of Imam al-Shāfiʿī in Cairo.
And Allah knows best.