-ocuser is the user in own/nextcloud, running it as www-data needs to be done manually
It currently only works if the syncthing folder is the complete nextcloud folder, you may need to change syncthing-owncloud/scanner/main.go at master · alex2108/syncthing-owncloud · GitHub to get something else (maybe you can misuse -ocuser to get some subfolder because I think the user only defines the path for own/nextcloud so for a subfolder your “user” could be user/path/to/subfolder)