Hi Peter,
Thanks for posting in the community.
Based on my test, when using the search box in SharePoint Online, there are two filter options for users to filter, File type and Last modified. For File type, you can tick the Other option to filter folders and other files. Also, if you click Organization, you can search in the whole organization. Since you know the folder name, may I know whether it works when you type the specific name in the search box and tick the Other option to filter?
In the meanwhile, if you want to create your own result type, here is the reference may help you.
Customize the search results page
If you have any updates, please feel free and come back to share with us.
Regards,
George