The "In folder" field will populate only if you are searching multiple folders, so make sure the search scope is anything different than "Current folder". An easier way is to do the search, once the results are displayed go to the View tab, and under the Arrangement section select "Folder" for grouping. Or just create a custom view and use it.
Hi,
Based on my understanding, you just want to search inbox folder without any results in subfolders under inbox folder. If I misunderstand your question, please correct me.
I suggest to make sure when you search inbox, the search scope is Current Folder. Then outlook will search just inbox folder without any subfolders under inbox folder.
If you want to search any subfolder, choose that folder first in directory tree, then choose Current Folder.
Best Regards.