Welcome to Spine!
In Spine, click the logo in upper left, then Settings, then Graphics:
Settings - Spine User Guide: Graphics
You want to uncheck Viewport linear filtering.
If you are doing a retro pixel style game where you render to a buffer, then write that buffer to the screen, you can check Viewport pixel grid to simulate the same in Spine. With this style, a pixel art game can be scaled up without the pixels in the original are from being rotated. You can enable and see how Spine behaves to see what I mean. For example, turn it on, zoom in, and then rotate an image and observe how the pixels are rendered versus with Viewport pixel grid off.
