Your camera took the image sideways and recorded a tag saying "this image is sideways, rotate it when you display it". For privacy, pictrs (image upload utility lemmy uses) removes all tags on upload. Adding support for rotating the image upon upload like many other image hosts do is on the road map, I'm sure. In the meantime use an image editor to properly rotate the image before uploading it.

Key's answer explains the root cause, but you'll find that many of the apps now deal with this for you while you're waiting for the web interface to get sorted. In fact as you're on lemmy.world you can use their alternative front end which I believe has this fix in place.

It came out unchanged as fate would have it!