What is the ruling on someone who completed the first two rak'ahs of the Qiyam prayer alone, then joined the Imam for the last two rak'ahs in congregation, and does not reciting a short surah in them affect it?

The prayer of this worshiper is valid, and there is nothing against him, because he missed the first two rak'ahs of the Qiyam prayer with the Imam, so he prayed them individually with Al-Fatihah only. Then he joined the Imam for the next two rak'ahs and completed the prayer with him. Those who consider reciting a surah obligatory in fard (obligatory) prayers say it is recommended in supererogatory prayers, because the sunan (recommended acts) of fard prayers are the virtues of sunan (supererogatory prayers).