Hi.
Word for Mac does not have a side-by-side feature by design; it only exists in Windows versions.
https://learn.microsoft.com/en-au/answers/questions/5640731/how-do-i-compare-two-word-documents-in-word-for-ma
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.
Also via https://learn.microsoft.com/en-us/answers/questions/5182619/view-two-word-documents-side-by-side-on-mac
- Hover over the green dot in the window controls to open a menu with three options: enter full screen, tile the window to the left, or tile it to the right.
- Once selected, the active document will occupy half the screen (full height) on the chosen side, while all other open windows will automatically resize and move to the opposite side.
- Select the second Word document to fill the remaining space next to the first window.
I hope this information helps. If you have any more questions, don't hesitate to reach out.
Otherwise, if your problem is resolved, please take a moment to rate the answer. Wishing you good luck!