BlenderKit: Download the FREE UV Texture Checker material
Freebie: UV Checker Map Generator - Toolfarm
Blender 2.7 UV Mapping 2 of 4 - YouTube
Download four free high-resolution UV checkermaps | CG Channel
You wanted some 3D artwork? You wanted something cool, something shiny? Something that puts a little dazzle in your eyes? No, fuck you. Here's a UV test : r/blender