i personally use photoshop to make sbahjs, which hussie also uses. i imagine you could also just as easily use photopea (https://www.photopea.com/) here is an excerpt of one i've made:

it really comes down to using photoshop as poorly as possible. filling things with the bucket tool, resizing images to create typically unwanted artifacts... a lot of stuff under the
"Image>Adjustments" menu is very useful. also very useful are things under the "Filters" menu, sharpen especially is good at creating crust. a tip hussie posted somewhere was saving an image as a low quality jpeg, screencapping the preview, then reinserting that into the piece. it's very fun, i recommend it. there's no pressure, because you're really just fucking around with how bad you can make something look