What is the purpose of Docker.raw file on Mac OS Catalina? I have Docker installed on my Mac OS Catalina and recently found very big file Docker.raw. It is 64 Gb. Is it really needed? And if so, why is it so big ?
The answer to your question is in the Docker documentation:

Disk utilization in Docker for Mac
Docker Desktop stores Linux containers and images in a single, large “disk image” file in the Mac filesystem. This is different from Docker on Linux, which usually stores containers and images in the /var/lib/docker directory.

The size of this file is big in your system because you have a lot of images and containers. You can reduce its site by pruning unused objects.