Steam Cloud saves don't sync

Turn Steam integration on again if you set Superposer up with a very early version: older setups pointed games at a tool name Steam doesn't sync saves for. Quit Steam and use Turn On… on the Steam Integration page.
A game you played before syncing worked may have local saves that clash with the cloud. If Steam shows a cloud conflict, stop and check which copy is newer before you choose.
Saves live in the game's own Windows environment, not in your Mac's Documents folder.
Some games don't use Steam Cloud at all.