How do I apply a stroke over an entire design, as shown in this youtube video??

[dnemeth01]

I am attempting to do what this YouTuber is doing.  He has a finished, flattened design that has a normal appearance, then he puts an outside stroke on the entire image to simulate vintage ink bleed.

 His instructions are streight forward.  What am I missing in this tutorial that will let me achive this effect?

I can apply stroke to text layers that I type but not a whole image.

https://youtube.com/clip/UgkxqV91tj6smvWZWSNJnO4ggXQlEX8kIivt

[dnemeth01]

This is an example of when I apply a stroke to a design when following the YouTube video to the "T."