RSYNC. How to do two way Windows sync nas4free?

Question

Backup

There is nas in the home LAN on nas4free. There are several machines on windows 10. Between machines, through us, you need to synchronize folders.
That is, roughly speaking, an analogue of dropbox in the local network. NAS acts as the main storage for backup data. If the first computer on Windows saves data to the synchronization folder, then on the second one, after turning on, this data also needs to be downloaded and synchronized.
On Windows I use the QtdSync program

Answer 1

Hello,
Syncthing, QtdSync, Dropbox, Owncloud, YandexDisk and the like are programs for synchronizing files between different devices. Roughly speaking, not to send them by mail. By the way, you can install Syncthing on nas4free and synchronize files from 10 machines at once.
But, synchronization is not a backup, since all your files are somehow connected to each other. On one of the machines, accidentally delete your file and the synchronization clients will immediately delete this file from all machines. Synchronization is just transport to one place, purely for convenience. And then you need to copy these files (manually or with a cron script or a flags script, here everyone comes up with their own) to another folder, to which no external programs have access. After this copying, the backup procedure will be completed for you.