hello99 : “If there is NO minhag hamakom today, as some here have maintained, then all Ashkenazim and most Sefardim who came to EY from other countries should maintain their minhag avos and keep 2 days YT.”
Good question there, but I think there is a difference.
Ligabei yom tov sheini, everyone who learns the Torah shebiksav and understands it, knows that the ikkar is that there is only one day yom tov. In chutz laaretz there was a gezeira to keep two days and it is continued to this day. But it’s not like there is a machlokes bichlal if yom tov is two days or one. In Eretz Yisroel, however, there is no such gezeira.
Ma she’ein kein by tefillin on chol hamoed, there are two different shitos bichlal and the shitos are not tolui in geography, whether it is Eretz Yisroel or chutz laaretz.