(If you don't mind, please, could we let let this go for now. )
Yes, we can probably forget about that. Unless for some reason you can't use the other workarounds. If not we would need to know what's causing the problem, so it can be fixed.
You're doing it correctly -- by the book, as they say. (I just can't figure out why the path doesn't work, but a duplicate does. But for now we won't worry about it.)
(The examples I found in the manual all show the text being put on an arc of a circle [can I call this an open path?], rather than a full circle [a closed path?])
Yes, that's absolutely correct terminology.
This is what works for me (using the file you attached earlier).
1 - Select the path
2 - Duplicate
3 - Delete the original (Alt + click + click to select the original when it's underneath the duplicate)
4 - Select both text and path (better to do by selecting one, hold Shift while selecting the other - this avoids accidentally selecting something else) (which could cause it not to work properly)
5 - Text menu > Put on Path
I'm not sure if you meant for the text to be inside the closed path. But when you reversed the path, that's what makes the text go inside. If you want it outside, just reverse the path again.
Bonus info:
You can change the location on the path, where the text starts, by a couple of different tricks. (doesn't work with centered text)
1 - Decide which node you want the text to start at. Select the node to the left.
2 - Break the path ("Break path at selected nodes" button on Node tool control bar) (looks like
).
3 - Select both resulting nodes (by dragging tiny selection box wih the Node tool))
4 - Join nodes ("Join selected nodes" button on the control bar) (looks like
).
Or if the distance is not too far, or if you want to text to start at a location which doesn't have a node, you could just add spaces before and/or after the text, to move it where you want. Or, if the path is a circle, you can rotate the circle to get the text in the right place. Or any combination of these would work as well.