Hello Lukas!
I believe this library should be a "library" type in your composer.json file, and not a "project type. Because of this wrong type, I get the following error on composer v2 since it is not a library.
Could not find a matching version of package lukaswhitephp-feed-writer.
Finally, on packages.org, it shows composer create-project as you mentioned "type": "project" in your composer.json file.

As soon as you change from "type": "project", to "type": "library",, packages.org will display composer require on your library packagist page.
Hello Lukas!
I believe this library should be a "library" type in your composer.json file, and not a "project type. Because of this wrong type, I get the following error on composer v2 since it is not a library.
Finally, on packages.org, it shows
composer create-projectas you mentioned"type": "project"in your composer.json file.As soon as you change from
"type": "project",to"type": "library",, packages.org will displaycomposer requireon your library packagist page.