Single file and folder uploads to nextcloud all go over the webdav API of the nextcloud server. For standard use cases like downloading and uploading, the [API](https://docs.nextcloud.com/server/latest/developer\_manual/client\_apis/WebDAV/basic.html) is pretty straight forward. When it comes to upload larger files, nextcloud provides a [chunking API](https://docs.nextcloud.com/server/latest/developer\_manual/client\_apis/WebDAV/chunking.html).