No it doesn’t.

Syncthing only needs to remember the current state of the files/folders it’s syncing. Not everything it’s every sync’d.

It does that by either periodically scanning the filesystem to look for changes since it last scanned (based on the file creation and modification dates that are stored in the filesystem), or it registers with the operating system to receive events when files are created, modified, or deleted.

When Syncthing notices a create, update, or delete, it pushes those changes to the receiver.

It also pushes whole files, not deltas. So it doesn’t care how the files changed, only that they did.

Even with hundreds of thousands of files to sync this is a relatively small amount of state as it’s just file paths and their create/modify dates.