I am looking for a Stud.io file for the 31120: Medieval Castle, but I am unaware of a place where you can find Stud.io files. Is there such a place?
I usually check at Eurobricks forums, as they have "Official Lego sets made in LDraw" topic, where community share LDraw files for digitally built LEGO sets. The list of available sets is rather limited since this a community effort after all.
At this point of time I couldn't find files for 31120 on EB yet.
The BrickLink gallery also includes a number of builds of official sets, however many of them aren't titled with the set name, but may include it in the description. Sadly there also doesn't appear to be any versions of 31120 yet.
You could download the instructions and have the fun of virtually building it yourself ;)
There is a 3D model available on Mecabricks, which can be viewed, edited or exported into various formats, if one of these fits your use case.