Everything I've seen suggests that boxplot provided by MS is only vertical.
https://support.office.com/en-us/article/create...
I have seen this utility you can buy to do horizontal box plots
PELTIER TECH BOX AND WHISKER CHART UTILITY
Quickly and easily create professional box and whisker plots.
Use raw data or compiled statistics.
Show or hide outlying data points.
Choose horizontal or vertical orientation.
Create box plots from within your own code.
Read More About the Peltier Tech Box and Whisker Chart Utility
Purchase the Peltier Tech Box and Whisker Chart Utility ($59 US)
http://peltiertech.com/Utility/CascadeUtility.html
Since they can do it, I imagine with some creativity you could do it also ...
... Oh, look at this, actually, they provide how-to instructions
https://peltiertech.com/excel-box-and-whisker-d...