R’ Chaim Vital notes that before Rabban Yochanan ben Zakkai, Rosh Hashanah in Eretz Yisrael was observed for one day. Tosafot suggest this was the case even in Ezra’s time, though the Rebbe explains it was an exception. While some propose observing only one day today, halacha does not support this view.

https://www.torahrecordings.com/rebbe/igroskodesh/015/011/5619