Only chassidim had separate seating in Europe. When R’ Moshe Feinstein married off his children, there was mixed seating. At yeshiva dinners, there was mixed seating. Separate seating probably became mainstream when a Rosh Yeshiva reached for a second piece of cake, and his wife scolded him for it.
There’s a story with the Chofetz Chaim written by R’ Pam about when R’ Meir Shapiro was traveling by Radin. He wanted to eat by the Chofetz Chaim, and asked for there to be separate seating. The Chofetz Chaim refused.