Can't sync to a folder in network

After reinstalling windows, and installing the latest version of the nextcloud client it is not allowing me to sync to a network folder.

I’m not mounting the folders as a drive, I just adapt my library paths to the network address. E.g. own data is \\dennis\data and so on. This was never a problem and was working until my current reinstallation.

I can select my target folder during the client setup, which ends up being \\dennis\nextcloud but then I get the error -1 B free space and can’t continue.

So during the installation I can skip folder setup. Opening the application from tray and trying to add the target folder from there, which is also selectable without any issues I get the error message “You have no permission to write to the selected folder!”

But this is wrong and I’m able to write to this folder. Any idea how to solve this?