You can open the file in another tab (Window -> New Window).

Doing so you have two copies of the same file. Then you can right-click the tab bar and select New Vertical Tab Group (or New Horizontal Tab Group, the one you like more).

Hope I understood you question..

Be on the tab you want to duplicate,
then click in the menu bar at the top on
Window > New Window

Finally drag & drop the second window to the the left or right side to show both views next to each other.
Et voila, there you have it :)

EDIT

It seems that this function is not implemented in all version of VS.
In my case (V 15.4.2 (2017), V 15.9.7 (2017) & V 16.2.5 (2019)) it just works fine.

Only vertically that I'm aware. When looking at the code, right above the vertical scroll bar is a small rectangle, drag it down to get a split view of the file.