Here are some sources which indicate that nevuah has ended.
Meforshim on malachi:
Mahari kara and malbim on 3:22, ibn ezra on the first pasuk, abarbanel also on that pasuk.
Avos D’Rebbe Nosson 47 says it stopped because of certain aveiros.
Radak on chaggai 2:5
pesikta Rabbasi 35
Maharsha on Yoma 9b, says nevuah stoppped because jews didn’t go back to EY when they had the chance.
Seder olam rabba 30 says that nevuah stopped by Alexander the great.
Rav tzadok hakohen in Resisei Laylah, 81b says that nevuah stopped when avodah zara ended, same as the gaon i mentioned above.
Michtav meliyahu chelek 3 pages 277–278
It’s not “what you heard in school”
Most things that are commonly taught in yeshivos are true. Rebbeim know things..there is a mesorah which you seem to want to undermine at every chance you get.
As for sukkah…i have nothing against chabad as a concept. I’ve outlined my reasons for being against divergent elements of neo chabad, some of which you agree with. They present a danger to mesorah and yiddishkeit, and almost the entire yeshiva world recognizes that.