I'm wondering how to achieve the pixelated edit on this photo? you can see it well in the background/sky of this image
Look at the edge of the of the flagpole and flag. See the haloes. Over sharpening.
Look closely at where it shifts from blue to grey. Streaks and banding.
This image started as a jpeg, then the range of light was tweaked, either by changing contrast, expoosure, brightness. When you do this, the editor has to do something with the roundoff errors. Often it means different colours.
Anyway you're trying to get this look.
I may have guessed wrong about which effect you wanted.
This what photos look like when they come out of my phone! To obtain a similar effect with a camera, raise the ISO pretty far up, say ISO 6400 on an APS-C or 25600 on a Full-Frame and then set noise-reduction to the maximum. This is what turns the noise into patches.
Some cameras do not have a noise-reduction setting that strong, it depends on the model, so you can still shoot at a high ISO and then apply a lot of noise reduction in software such as Lightroom. Make sure you reduce color-noise, not just luminance noise if your photos show colored grain.
It looks like JPEG artifacting. Here's how I tried to replicate it:
Save as for web, JPEG zero quality, but then set the image resizing method to bicubic sharper and expand the image by 101% to get it crispy.
Then, re-open the exported image and apply the sharpening settings:
Result has the patterned mosaic look to it: