But i found my own solution, i went into the flow chart and edited the "Upload GDrive file" block. In the "google account" input argument i removed the 'account' variable and chose there my google account statically (without user input on startup).
This worked for me finally.
Had to create a temporary new flow and add a GDrive list block. This then triggered the authorization proccess. After that, the former flow started to work again.
Also received notifications from Google about Automate being authorized.