While you wait for my colleague to take over the ticket, let me try to help you with the issue quickly.
I am not sure what copy of templates you mean, but if those are some templates you created by translating the theme, you can easily access them as any default language template. For example for Pages, go to Pages > All > Choose a language to filter that language.
I understand your suggestion about the menu, but I see there is another problem.
In WPML > Translation Management, when I filter on ‘Template’ and ‘Polish’, I see some templates. Single Product, Single Post, Blog Home. When I edit the Single Post-template, this template is opened, and I can edit it. It does not affect the English (default language) template.
The problem now is that I don’t want these variants of templates in different languages to exist. It means that every change in the template must be set in all languages. For example, if I want to change the padding of the content.
Technically, yes you can delete the translations. To do this go to Elementor -> Templates switch to the secondary languages and delete them.
However, I do not recommend doing this -- to ensure the templates display as expected it should either be translated or duplicated into the secondary languages.
When your templates are translated the changes you make in the default language will take effect across all languages, it simply requires accessing the translation and re saving it when you are prompted to do so.
When you duplicate that is not needed as it's a duplicate.