That’s odd. Any error?

Federation from your instance Lemmy.world to the instance the community is on (programming.dev) is healthy, so that doesn’t seem to be the issue.

How far did you get? Any error?

My guess would be that you’ve tried to upload an image that is over the size limit - I think this is imposed by your own instance (Lemmy.world), and I’m not sure what the size limit is but I think 5MB per image is pretty common. If you drop the image size or upload elsewhere then link it, does that work?