I have looked through the app I use (mlem) and the web interface but I can’t figure out how to give a link post an image, as when I try to put something into the image section it replaces the link.
So how is it done exactly? Is this some setting, special script or app feature I don’t know about? Or have I missed something?
This isn’t directly possible. You can add an image to the body of the post using the
![alt text](https://example.com/image.png)
formatting. Lemmy automatically chooses an image to display on link posts. You can’t override this on Lemmy 0.18.4, which Beehaw uses (I believe it’s possible on later Lemmy versions, but the official UI doesn’t support it on those versions).