Share a folder via ftp

As long as we're talking about within the same loca area network, File Sharing should be fairly similar (if I remember correctly) though FTP may not be an option. You can use AFP or SMB protocols instead.

If you were sharing stuff via FTP to a computer at another location, you were probably using an FTP server as an intermediary, or using advanced server software on your Mac to make it visible to the world.

FTP is not very secure, so yes, DropBox is safer.

You should indeed use Dropbox, Google Drive, OneDrive, or other commercial cloud service to share files with clients. Not only is FTP a completely insecure protocol but you would also need to allow external network traffic in through your router/NAT firewall (another bad idea).

Modern cloud services are exceptionally suited as a replacement for the old methods of exchanging files with clients through FTP.

If you ever decide that you do need FTP then I would highly recommend setting up SFTP on an external hosting provider (such as a web host you may have) instead of using your local Mac. Allowing external FTP traffic from the Internet to reach your local Mac (unless you limit IPs at your router) will result in many, many unwanted probes trying to break in.