composer require 'drupal/varnish_purge' does not install dependencies

The info.yml file is misnamed and does not match the name of the module. It should be named "varnish_purge.info.yml".

please Review

"This is not a bug, it's a feature".

From the module page, second paragraph:

Project name and module name
Because of some bad naming in the start - the project name is varnish_purge, but the module itself is called varnish_purger. Sorry for that, but it's hard to move namespace after you have registred one.

You have to use

composer require drupal/varnish_purger

The proposed info file rename does not fix this, and also ignores config, schema and others files that have 'varnish_purger' in their name or namespace.

Just leave it, until there is a proper solution to fix the project name(space).

The proposed resolution is to add a composer.json. The MR does not match the proposed resolution.

The rename of the info.yml file is out of scope for this issue

FYI: the composer file was removed intentionally by maintainer: https://git.drupalcode.org/project/varnish_purge/-/merge_requests/12/dif...

https://git.drupalcode.org/project/varnish_purge/-/merge_requests/12/dif...

In the commit message the dependencies in the info.yml file are assumed to resolve automatically. This assumption is incorrect for this module.

True, but this module clearly has a history concerning that part, so you might want check why this was done.
Beside, if you clearly know what needs to be done, why don't you provide the solution?