I have a desktop at work and one at home. I want to use an external ssd to make a backup (probably using rsync) of one of this desktops, and then use this backup to update the files and folders in the other desktop. Note that it is not a backup of all files and folders, but only some of them that I use for work.
For example: I do some work at home, use rsync to make a backup in an external ssd and then use this backup and rsync to update my folders and files at my desktop at work. And of course, this should work the other way around.
Also, I want that the deleted files in one desktop to be deleted in the external ssd and in the other desktop.
For backups, I recommend using BorgBackup because it saves a lot of disk space and can encrypt the backups by default. There is a GUI tool called Vorta for this.
Compared to rsync, Unison is fully bi-directional and allows the user to detect and reconcile conflicts when both copies of a file have been changed since the last synchronization.