I have enebled the windows feature 'controlled folder access' (In ransomware security) which denies write access to most destinations until I whitelist the app or the folder. When I start zettlr portable, it tries to write something to %userprofile%\OneDrive\Dokumente which is denied by windows and the zettlr app is aborting its own startup.
I believe zettlr portable MUST NOT write anything to my systems documents folder automatically. It should stay on its installation medium
Author of zettlr said, he is not responsible for the portable apps integration:
The PortableApps release is a third-party service with whom I do not have any communication. I do not know what they do to their binary, and hence cannot help out here. Please try to get in contact with them instead, they may be able to help you. By default, Zettlr only needs access to its data directory and any workspace/file you open with it. There is a way to modify the genuine binary from our website/here on GitHub so that it becomes portable. Please refer to this guide: https://docs.zettlr.com/en/portable/