If I use the following web link in a draft, preview displays it perfectly:
I read in the forum that the same should be true for a direct dropbox link. If I click on a direct dropbox link in a draft, the image will be displayed, but it is not displayed if I click on preview
Have you made sure that you have amended your download parameter from 0 to 1 to make the normal link a direct link?
It works for me as shown here.
how it works if I change 0 to 1 as you suggested.
In Drafts Mac, I can now display text + images in Marked 2 and also export as RTFD (to include images) if I want to create a Scrivener document.