After the Sinai was captured in 1967, was Yom Tov celebrated there for one day or two days?
Yom Tov was celebrated there for only one day. Much has been written on the subject of how to determine the criteria whether one or two days are to be kept for places within the vicinity of Eretz Yisrael but have not been known to be settled. I will suffice with the opinion of Rav Tokazchinsky zt"l ,who wrote a lot about the customs of Eretz Yisrael , that all places that are in the boundaries of Eretz Yisrael as elaborated in parshat Mas'ei are part of Eretz Yisrael, and therefore only one day is to be kept there. Being so, Sinai is part of Eretz Eretz Israel and only one day is to be kept there. See (עיר הקודש והמקדש כרך ג׳ פרק י״ט