Hello Mikhail,
Indeed, I noticed the wording in the footnote has been changed. It is now:
"Parallels Desktop 19 supports only macOS virtual machines created on a Mac computer that supports the operating system as a host OS. Feel free to give it a try if you need such a virtual machine, though please note that it might not work."
Maybe it's me but this doesn't clarify it at all. The first sentence alone: [Parallels 19] only supports virtual macOS machines what were created on a Mac computer (in a version of Parallels I presume) that supports the operating system as a host OS.
In other words, to create a virtual Mac OS X 10.6 machine, I would have to create it using Parallels 7 on a Mac OS X 10.6 system and only then will the resulting virtual machine be compatible with Parallels 19. And if I would create a virtual Mac OS 10.6 system on a modern machine running Parallels 19 it will be totally unclear if the virtual machine will work or not. I find that very peculiar and quite worrying.
I've been running virtual Mac OS X 10.6, 10.8 and 10.11 machines (many) without issues in various versions of Parallels for years now, up to and including Parallels 18. Why is Parallels 19 suddenly different?
I guess I will have to stick with version 18.