In case anyone is interested, here is a bit of background on why I wanted this utility.
I'm an amateur photographer and shoot raw files, which are processed in Lightroom (LR). Once edited to satisfaction, the files are exported out of LR as JPG files. Typically they go into a subfolder of the folder holding the raw files. There can be many variants on the file system, but this one works well for many of us. It is a good system - photos are logically stored and can be found back later.
But there are times when one wants to pull those JPGs out of the folder tree and put them somewhere else. For instance if I am travelling, I might want to have the JPGs along but don't need or want the raw files. Copying the whole tree just to have the JPGs can be done, but that is a lot of stuff! My 2019 tree currently takes up 56 GB. The 2019 JPGs are only 156 MB.
Of course it is easy to copy files with a particular extension out of a folder tree, but the challenge here was to retain the descriptive names of the parent folders. That is achieved in the solution provided by BC_Programmer. Thanks!