How to get bundle machine name when viewing the creation form?
Writing your own question is always useful.

I may have a solution, even if you may have something different, so please share.

I have built a Views block with a custom text (my link) as unique field (only show one result, you do not need to repeat the link, of course).

I have added a contextual filter based on content type with a default value provided by url, raw value, third component (node/add/mybundle_name), with case transform in lower case.

My link looks like :

&lt;a href="/existing-nodes?type={{ raw_arguments.type }}"&gt;Clone existing&lt;/a&gt;


And it works.