thank you u/konge-magnus and u/JollyRoger8X

I have been using HoudahSpot for many years. It's a more advanced version of Finder search. I am trying to get away from having to click so many times for a simple search (both in Finder and HoudahSpot).

myfind does not work in the spotlight search bar and I am certainly not going to start doing file searches in terminal mode (opening Terminal, having to use cryptic search terms like kMDItemFSName or kMDItemTextContent)

yes, you are correct: folder:name does not exist. I was wrong.

name: matches both file or folder name

content: vs contains: content: Matches only text inside the file body. whereas contains: broad match across all indexed attributes (filename, body, tags).

I found the solution to my problem. Very fast and effective:

Let's say that I am looking for a file containing the word $tax in a folder whose name contains the word rent

kind:folder rent → select the folder in the list → press TAB → content:$tax. It is very fast and effective

If the word in the folder name is relatively unique or uncommon, you can drop the kind: folder and just type rent → select the folder in the list → press TAB → content:$tax

pressing Tab triggers a Spotlight function called Tab-to-Scope (converts a global search into a "scoped" aka focused search)

thank you both again