2
A kuwahara shader would be a good start, with bright colors as an input. First hit resulted in this:
Shader "Unlit/Oil Painting"
{
Properties
{
_MainTex("Texture", 2D) = "white" {}
_Radius ("Radius", Range(0, 10)) = 0
}
SubShader
{
Blend SrcAlpha OneMinusSrcAlpha
Pass
...
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