How to use pin in iMessage is baffling to me in iOS15

OK I'm not dumb, I don't think. I can't figure it out.

I'm supposed to hold on a picture or link or content sent to me in iMessage and see a pin at the bottom so I can pin it and then have it in a section when I click on the picture of the person in iMessage.

• I click on a picture, I don't see it, but sometimes I see it (I think - I saw picture in the Pin summary)
• Does it work on files (like a DOC file message to me)
• I click on an article link and I see it
• Doesn't seem to work on a message either?

This is from my iphone

I'm baffled.

Then I try it on my Mac laptop -- not there either - for example this is a Live Photo and nothing there