I was told that Apple does not allow app generated from open source to be posted on the Apples store, is this true?
If I develop an app using the GPL license of the Qt framework, can I put the executable on the app store?
It depends on the gpl version and what it allows.
Which version of the GPL license is that framework licensed under? Is it the one where the distribution license requires that you are required to distribute the source code for your application, and that the Free Software Foundation has stated is incompatible with how the App Store works?
If Apple has a statement prohibiting that software, it is in part because you can't (without violating the terms of that version of the GPL) legally ask them to distribute that software.
From one of the discussions of GPL v2:
Section 6 of GPLv2 says: Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein.
When the App Store terms prohibit commercial use, general distribution, and modification, these are exactly the kinds of "further restrictions" that are not allowed thanks to the last sentence here.
This is a crucial part of the GPL's copyleft. Without this section, it would be trivially easy to keep freedom away from users by putting additional requirements in a separate legal agreement, like Terms of Service or an NDA.
Section 6 is not legal minutia: if you take it away, the license would completely fail to work as designed at all.