What is the program for synchronizing only changed files via a USB flash drive?

Question

Data synchronization

Task: synchronize two computers (No. 1 and No. 2) via a USB flash drive.
The workflow is set as follows:
1. We work on No. 1.
2. At the end, copy everything to a USB flash drive.
3. We come to number 2.
4. We transfer from a flash drive to it.
5. We work on number 2
6. At the end, copy everything to a USB flash drive.
7. We come to number 1.
and so on in a circle
Now, to facilitate copying, FreeFileSync
is used (by the way, not one, but many directories are synchronized, and on different computers some of them have different names).
But the fact is that the number of files is growing, and the flash drive is no longer enough. And most of the files are edited quite rarely, so they lie on the flash drive as an unnecessary load.
I would like to find such a software that would store information on a flash drive in any format about what files are already on another computer and would copy to the flash drive only files that have changed in size / date / checksum.

Answer 1

Yes, unusual behavior. With this approach
, why not use network synchronization? GoodSync , BittorentSync

Answer 2

having tried many programs goodsync.com is the best, others did not even do a simple one (deleting a file if it was deleted in the original folder). and the settings are many and clear.
Many recommend the free allwaysync.com