Thank you so much
That's exactly what I am looking for.
Regards

SFTP protocol works as remote file system. You always (even when downloading/uploading a complete file) operate with file chunks using the SSH_FXP_WRITE and SSH_FXP_DATA requests. That allows you to operate on any part of the file (contrary to other file transfer protocols).
Refer to SFTP specification:
https://datatracker.ietf.org/doc/html/draft-ietf-secsh-filexfer-13

Yes Martin, I understand.
Can you please advise which keyword to search for regarding SFTP protocol related to the issue?
I appreciate if you can share a link.
Thank you

WinSCP does not have any commands to upload only parts of a file. I was referring to SFTP protocol in general.

WinSCP can only upload additions to the end of a file.

Hi Martin,
Thank you for your reply.
Kindly; is there any reference to what commands I can use over sFTP?
What commands that WinSCP support?
I guess it will be some limited commands.
I am about to do a research on the topic; I will share it with you.
So any help is appreciated.

Any reference please?
I googled and couldn't find.
Thank you
Regards

A) It's possible with SFTP protocol without any changes on server-side.
B) You can write a WinSCP extension for that. Actually a part of this is written already:
https://winscp.net/eng/docs/library_example_zip_and_upload

Hi WinSCP,
Love WinSCP, amazing ftp software and so fast!
I have two ideas:
A)
in this scenario:
When a single user working on a file (Lets assume a PHP file).
Some times we amend a minor changes. Lets say we forgot a semi coma somewhere.
Normally we re-upload the whole file.
Lets say the file size is so big (1 MB) (Just assumption)
Is there a way to upload the changes only?
i.e. the difference between two files in local machine and remote server is just one character. So is it possible somehow to add a new feature to the client and server to understand this changes.
I can't propose a mechanism to achieve this feature; its only an idea that comes to my mind and personally it makes sense. But don't know much about possible technology implementation.
If this if to be implemented; I think needs changes to client application and server application to adapt.
I am not sure if this is valid; but I guess this needs artificial inelegance technology.
If to be implemented; this will amazingly increase upload speed for a single user having lots of files of type of PHP in our example.

Can't be sure this would work for binary files; but at least can you consider my idea for ASCI files?
B)
In normal routine, when I need to upload a big number of different files.
I zip them into one and single archive.
Upload to server. Then from the server panel, I unzip.
This so much reduce upload time.
So, technically; is it possible to let ftp client zip files before upload, then at server side, the ftp server will unzip in the same folder structure.
Do you think this could be two good ideas?

Your feedback and input in my ideas so much appreciated.
Thank you so much
Sincerely,

Disclaimer:
This is my own idea and I had shared it with some other websites and planning to prepare a research paper about it.