How can I create Ubuntu bionic or focal Vm's using Vmbuilder tool?

You might want to give Packer a try. This is a tool that make headless installations from ISO images and can generate multiple types of VM images.

Basically you would do something like this:

Write (or find) a build template. These are JSON formatted and can be named anything, like bionic-production.json or focal-uat.json.
Confirm that the template is complete:
```
packer verify focal-uat.json
```
Build the image:
```
packer build focal-uat.json
```

There are a remarkable number of output formats and builder templates available for you to start with.

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