They're probably saving as PNG images. But showing as a screenshot. The resolution should be correct at 1125X2436. That is until uploaded on the forum. Then they're cut to 946X2048. But you can reverse it back using the Image Size app.
After reviewing the hundreds of screen shots, I'm surprised that only two others (steveh552, TheRewardisCheese) follow my pattern of organizing apps alphabetically. I group apps according to how often I access them and then alphabetize within groups. And yes, I realize that's highly OCD.