In TeXstudio 2.12.14, the embedded pdf viewer is displayed to the right of the editor. Is there a setting that allows the pdf viewer to be displayed either at the bottom or top of the editor?
The editor part of TeXstudio can be split horizontal or vertical see texstudio split screen
The viewer Section can not but you can as you know have one imbedded window and any number of floating viewer windows including an external one. Using Windows split screen and snapping makes these fairly easy to position and there were many 3rd party apps to control how screen division can be locked into profiles for multiple apps. but most of these were abandoned as windows 10 screen features improved.
For other ways to run dual compile using split editor and viewers see
https://tex.stackexchange.com/a/473233/170109 (dual sessions/instances)
https://tex.stackexchange.com/a/472480/170109 (split editor) and
https://tex.stackexchange.com/a/471069/170109 (split viewers)
In TeXStudio, the viewer windows is incorporated to the program window, but can be individualized and even, given to an application like Sumatra. I ignore if the new arrangement can be permanent, but TeXStudio can remember its window configuration, which could aleviate its repeated use.