I have the Nextcloud AND the iCloud Drive sync running on the same folder. There has been no issue at all, it really worked fine.
Recently my harddisk got full (because I imported loads of photos to iPhoto) and my iCloud reduced the size of the files in the sync folder to 0B. I guess it is something like virtual files in Nextcloud.
My question: Can Nextcloud deal with the virtual files from iCloud? Or is it a real bad idea to use both sync clients on the same folder?