I had a strange one a few months ago. I was sitting on a high point glassing and while looking through my spotter, noticed this small, metallic looking thing moving up my fov. At first it was almost like an eye squiggly, but I zoomed in a little and it was an object moving in the air of greyish/white/metallic color, looking roundish from where I was.
It moved up a hillside until the sky was in the background, then started back down toward the ridge and trees, all at one constant speed. I thought if it was a bird, it would land in a tree and disappear. It coasted along the ridgeline, still at the constant speed, before swooping upward into the sky background again. It then stayed at a fairly constant elevation moving directly away from me with a sky background until I could no longer see it, at the same constant speed.
Some may say mylar balloon, but I can’t imagine a balloon moving like this object moved. Also, it was far enough from civilization that I can’t imagine it was a drone, and I couldn’t make out any typical drone features on it. It was weird enough for me to write a note down in my phone so as not to forget the experience. Our predominant wind is typically from the west, and the object moved into a west/sw direction, and I didn’t pay attention as to what the wind was that day, but if I remember right, it was on the west side of my face when glassing. Who knows!