Hello!
Is it possible to paint PBR materials in Unity by using Polybrush like in this video in UE?
Also, what is better solution to paint dirt on walls when I have a modular scene made from multiple walls, painting it by using Polybrush, in Substance Painter or by using decals?
It depends on your shader, not on polybrush. If your shader blends layers based on vertex colours, then polybrush can help (along with any other vertex painter).
Many people have done this for years in Unity. Your task is to find a shader that blends based on vertex colour. Moved this thread to world building forum.