I'm making a private framework for third party developers, who do not need to know anything about servers, URLs and so on.
I need to make some settings for ATS, but it seems like changing info.plist in that framework's project doesn't work.
Am I doing something wrong or it's supposed to be like this, that I must not manage ATS in scope of my framework?
The ATS configuration applies to the final app, not any particular framework in it, so the info.plist that will be used will be part of the project that uses your framework.
It is up to the developers responsible for that project to add the appropriate keys to their info.plist. There is nothing you can do as the framework developer aside from documenting any required ATS configuration.