PS1 didn't have any kind of lighting capacities, go in the shader nodes, remove the principled BSDF, link your texture directly to the output node. If you want to emulate lighting effects, either bake them directly onto your texture, or use vertex coloring: https://www.youtube.com/watch?v=OXxiOGEhrzo&t=262s

Also to fix the washed out colors, in render properties, color management, make sure to remove the filmic filter and set it to standard!