Whether clonning of an existing "work"- qube has security flaws?

Hi, welcome to the community!

A cloned qube is totally independent. You just copy the contents and preferences of a qube and create a new one. See also: Better Understanding Template Cloning.

Secure copy works for any pair of qubes: How to copy and paste text | Qubes OS.

You should create a separate topic for that, so other people will be able to find it, too. What does it write when you run it from the command line?

See here: https://www.qubes-os.org/doc/glossary/#standalone

By default, there are no standalone qubes installed. They only appear if you create those. Such qubes are fully independent operating systems, with their own root and home partitions.

HVM is a virtualization technology, which is recommended for not officially supported operating systems.