Temporarily Exclude a Folder from Synchronization

I am using macOS with the current NC client verion 3.11.1. I have set an automatic sync of my local ~/Documents with NCs directory Documents. Now I want to temporarily exclude a specific local subdiretory from syncing. But when I in NC client > settings > choose elements for sync uncheck the box left of the respective directory in the bottom of the window a message appears saying, unchecked folders would have been deleted form local file system. But, this must not take place. I do only want NC to exlude such folder from sync with NC.

How can I do that?