Is it possible to select fields for the export?
For example: When i click button it shows me a popup, where i can select content i want to attach to the exported file.
Currently this is not possible. You can always build a view that contain only fields you need. Or select fields when configuring view's display.
Developers needed to choose between GUI on export and unattended processing. They choose automation capabilities, and for good reasons - large exports can take a long time, so it makes sense to trigger them at night using
If you believe there should be such option, then you can fork project - it's opensource, GPL v2, so you have full right to do so. You can also file a feature request in module's issue queue, but personally I don't think it would be implemented by maintainers. If you will provide ready to use patches, then maybe.
May be Views Dynamic Fields will help you.
From the project page:
The Views Dynamic Fields module provides a filter for use with Views module. This filter allows the user to pick and choose which fields to display for a rendered instance of a view for that user. This provides a customized view instance for each user.
This module provides additional advantages when used with the Views Bonus Pack module or the Views Excel Export module to generate an xls file from a view. The xls file will only display the fields you have chosen on the rendered view instance in browser.