Syncthing do sync with blocks, but database is not like text files, it’s operation is not like appending texts at the end of file.
If an item is inserted into the middle of the database, then the whole data follows would have a data position shift, then these blocks follows would all need to be delivered.
You should not use syncthing to sync databases, as many database don’t consist of only one file (the syncthing database itself is such a database), which will result in inconsistent state if not all files are synchronized at the same time.
Database files are also often blocked for the time the using software is running, so cannot be synchronized in that time.
Also, databases use mmapped files, which are not real files (atleast while they are open), so syncing them will probably lead to corruption and data loss.
You might be better of looking at rqlite or something
We have various optimizations to handle inserts in the middle. Though I’ve yet to hear about a database that would do what you describe. And yeah, don’t sync databases.