I searched it up on Google and according to AI:
In the context of Roblox, "retroslop" refers to the practice of creating avatars or games that attempt to recreate the look and feel of older versions of the platform, but often with a poorly executed or inauthentic result, typically by over-relying on modern items or accessories. It's a term used to describe the "slop" or poorly executed versions of the "retro" aesthetic according to a YouTube video.