Polylang deletes subdomain

I have installed Polylang on my website. The site has four languages, the main language is English.
If I now switch to another language, then the subdomain is swapped for https://www., although the correct subdomain is still entered in the link.
If I deactivate the plugin and call the page in e.g. German, then the subdomain remains.

Where can I set or what code do I need so that the subdomains are preserved?

Thanks,
Tom

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