You can open about:sync-log via the location bar to see if recent Sync logs are available. You can upload the file to a website like Pastesite if you can't post the content of the file in a reply.

• https://pastesite.org/

How long did you let sync remain active? Sync isn't a backup system it only sync data across devices and it's not instantaneous as it takes time to update the sync data.

It syncs to Sync servers and not device to device though.