Is it possible to use syncthing as a FTP tool to synchronize web space with local space?
I think that would be a very bad idea - it’s been discussed a few times on this forum.
FTP tells you when it’s finished, and any errors that occurred. Syncthing doesn’t, and so you don’t have the same guarantee that you’ve actually updated everything.
FTP is still a bad tool for the job. Rsync is better, but you really want a proper deployment solution (capistrano comes to mind, but there are others) which atomically updates your files, runs hooks, migrations, etc.
I bet nobody understands your question as its very vague. The documentatin explains what syncthing does, and you can decide from the documentation if it can be used for your usecase.