To my knowledge, praying surah Fatihah in the last 2 rakahs of fardh namaz is sunnah, but is it WAJIB to stand as long as the surah Fatihah is read?
Al-jawab billahi at-taufeeq (the answer with Allah’s guidance)
The worshipper has the option with respect to the last Rakahs of the Fardh prayer. If he likes he may remain silent (that is possible to say three Tasbeehat in it), but if he likes he may recite (Surah Fatiha) or he may even offer glorification (Three Tasbeehat). However, It is preferable to recite Surah Fatiha, as compared to glorification because Prophet (Sallallahu Alaihihi Wasallam) used to do so persistently.
Consequently, there is no obligation of rectifying an error (missing the recitation) through Sajdah Sahwa.
(Hidaya, Book of Prayer)
And Only Allah Ta’ala Knows Best.