Jerboa’s not too bad, as the URL field is the same field the link to your uploaded image ends up overwriting, but I swear I see people making this mistake every fucking day. End up posting just an image when they wanted image + link.
Apologies, as I’m sure there’s proper channels for this, and open source projects tend to not have the best UIs. Just shouting into the void.
Better yet would be for the backend software to allow both an image and a link.
That is possible
To get a link post with a custom thumbnail, you add the link and put the image in the thumbnail field.
To get an image post with a link, you make an image post and put the link in the post body.