Linux App to sync phone data to smb mount

Xplore file manager.
Option called file sync.
Available in the free version. If you like it, do support the dev. Certain features are behind a paywall.
 
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So these are the options available.

It can't create folders (atleast that I know of). But if you're on linux, you can create a folder daily and move the old one to one named by date.

ie.) Phone backs up to a folder called "Backup". Each day at midnight, the folder is renamed to "Backup - DDMMYYYY" and a new folder called "Backup" is created.

This is the best workaround I can think of.

But in this case, I don't think you'll be able to backup only missing files.