I notice that when I first load up an image in Photos or some other image viewing application, it seems blurrier for a short amount of time before sharpening. How do I deliberately replicate this blurriness? I've tried tinkering around with Gaussian blurs and also with scaling down the image and then decreasing PPI before exporting but can't seem to get it down. The effect seems to decrease aliasing and gives the overall image a less sharp look.
Try to use Filters>Blur>Pixelize with a block one pixel wide and four pixels high (you have to unlink the entry field (chain link icon on the right) to allow their values to be different).