Like Scott M said, it's because of the metadata stripping.

Temporary workaround if you do want to strip all other metadata:
On the protonmail app (linux at least) you add an image, strip the metadata, save the image, set correct rotation in another app, and finally re-add it but without stripping metadata this time.

But this is quite a hassle especially if you have to do it often so hopefully rotation will be added soon (and/or rotation is not stripped).

Yes, please, allow rotation of photos thank you

Rotating photos is a simple yet powerful way to enhance how your images are viewed and presented. Whether you're adjusting a picture taken at the wrong angle or creatively flipping https://testewebcam.com.br/ it for a fresh perspective, rotation helps bring clarity and balance to your visuals.

I also have this issue. When attaching images inline or as attachments and you use the option to remove EXIF metadata, it also removes the EXIF rotation data from the image, which results in upside down or sideways photos when attaching to emails. This should be corrected. Either don't remove that data during the EXIF swipe or give an option to retain it (remove all metadata except image orientation).

Attaching photos taken from a phone camera is pain now because of this. I love the option to strip metadata, but it shouldn't cause this new problem.