A family of Microsoft word processing software products for creating web, email, and print documents.
What AI doesn't seem to know is that Mac Word does not have a side-by-side option. You can use Window> Arrange All but that arranges the two windows vertically. The OS features which provide the type of arrangement you're looking for is in Window> Move & Resize.
Also, the Split feature displays the same document in 2 sections of the same window one above the other. It doesn't pertain to separate documents.