Zettlr tries to wirite in %userprofile%\OneDrive\Documents
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: