Camera app should negate the need. most pictures are of people and scenary, and 99.99% of the time the intent is to take the photo in the right order.

Simple totally offline ONNX models exist, whcih should make it trivial to categorize the right orientation. Acceleometer/magnetometer can feed this, but should not be the default.

Just do this and avoid the hassle of rotating at all!

Similarly, why don't photos get auto-straightened, maybe with an option to revert to original? I spend too much time aligning the horizon properly on snapshots that I took while cycling. The phone even has the data from the rotation sensor, so this should be fairly easy to implement.

This is so true. Sorry you got downvoted.