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I cannot find my sync button in LR!
Lightroom-Desktop (v6.5 on a PC) does not have a 'Sync' button (as does Lightroom-Classic). Lightroom is always syncing to the Cloud. That is how it is designed.
Lightroom does have a Cloud icon to indicate the state of your Cloud storage and syncing progress-
Or if you are referring to 'syncing edits between photos' -it is the Three-dot icon that opens the Copy&Paste dialog-