The answer is already built into MacOS. It is called "smart folder", which is basically a view on a directory based on a query. So you can query all files in your subdirectory recursively, with a "kind" restriction if you like. Here is a nice intro to smart folders

The answer is already built into MacOS. It is called a "smart folder", which is a view of a directory based on a query. So you can query all files in your subdirectory recursively, with a "kind" restriction if you like.

How to create a Smart Folder

• In the Finder on your Mac, choose File > New Smart Folder.
• Specify the criteria. ...
• Click Save. The system asks for a name and location for your Smart Folder.

There are excellent videos on the internet introducing smart folders. Check them out.