Can I change the Linux kernel that Docker uses on macOS?

Q1: Can I change which Linux kernel that Docker uses on macOS?

Safe and simple answer: No. Unless you want to mess-up directly with the Hyperkit VM that docker desktop for Mac is deploying for you when installing. I don't use Mac, I have no clue it this is even possible and strongly suggest you don't walk that path unless you seriously know what your are doing and are ready to reinstall everything if this breaks.

Q2: When does Docker upgrade the Linux kernel version?

When that change is incorporated to a new release and announced on the Docker for mac release notes. Latest kernel upgrade was made on 2020-05-27.

That being said, docker only uses the underlying kernel of the OS/VM where it is installed. If you really need a different kernel for a very specific reason, you can always deploy in parallel your own custom vm with the exact kernel you want, install a docker engine there and use it.

https://stackoverflow.com/a/65844573/8818399

Docker uses its own patched Kernel (along with a specialized Linux distro) called linuxkit in Docker Desktop. It is mentioned in https://hub.docker.com/r/docker/for-desktop-kernel.

I am able to find kernel, initrd.img and cmdline in a folder called linuxkit inside the application folder of my Docker for Mac installation.

Simply build your own Kernel with the instructions/patches of linuxkit and replace those files.