You are correct—the links work when clicked from within DT. I do most of my Markdown note editing in Typora and usually end up clicking on links from within Typora. Clicking on the hyperlink within Typora results in the link not working, as described previously, while clicking on the link in DT’s preview pane works.
I just checked clicking on the link pasted into a RTF document in TextEdit and that, too, works. So it looks like there is some, rather weird, hyperlink-clicking bug in Typora. I will check with them.
Thanks for investigating on my behalf… much appreciated.