MacOS – Is it possible to display a Smart Folder as a stack in the Dock

Here's the steps I used to do what you're looking for which seem to be working the way you want.

Open Finder and click File > New Smart Folder - or press ⌥⌘N

Then setup as I have in the screenshot below and click 'Save' near the top right.

Then, when the little drop-down menu appears for you to save, select the options like I have below.

Now, you'll get a window left behind like this.

Now, close your new Smart Folder. Then in Finder, open a normal finder window with either File > New Finder Window or ⌘N

Your 'TV' Smart Folder will be listed under the 'Search For' section on the bottom-left if you expand it out, like so

You need to change the icon of the folder that contains the items in the stack. This can be done in several ways, but perhaps the easiest is to start by navigate to the folder of the stack, change that icon, and set the stack to display the folder instead of the contents.

Click the stack, click "Open in Finder" in the stack, and then press the keystroke ⌘ + ▲. The key press will take you "one level up" in the directory hierarchy so that you are now looking at the folder that houses the items in the stack.

Next, select the folder (If it's not already selected), and "get info" on it, by typing ⌘ + I, or right-clicking and selecting "Get Info". At the top of this window will be a miniature icon of a folder. You can click on this and copy it via the keyboard shortcut (⌘ + C), or paste in an image that you copied from somewhere else.

Finally, you need to right-click on the stack and set it to display "folder" and not the stack contents.