It happens that I noticed a text insert I had pasted in an image in Preview 7 (Sierra on MacBookAir had been rotated I don't know how this happened but the text insert is definitely not horizontal. So there must be a way to rotate inserts. I haven't yet found out. Can anyone tell me?
You can rotate inserts and annotations, like text boxes, rectangles or signatures, by arbitrary angles:
Hold the Command ⌘ key and rotate the selected annotation with two fingers on a trackpad.
As far as I know this only works with trackpads and is undocumented. It works on macOS High Sierra.
This is from an apple communities question: How can I rotate the text box in Preview