There is NO WAY for you to sync DLC/Just as planned (basically any purchases) across different platforms.

There is NO WAY to restore a save to a previous state. (You can only overwrite it.)

There is NO manual save feature. (Only autosave for now)

There is NO save editing feature. (No create different save profiles/delete saves)

Autosave/Synchronization will occur when you

• Launch the game then enter
  
• Exit from a song (even if you didn't finish playing it)

The developers are still working on improving their real-time syncing system. And there are some issues at Google's side making it sometimes difficult to login Muse Dash with an google play account and syncing saves in real-time with it. So for now use other services such as TapTap/Facebook to avoid syncing problems.

• Step 1. Open the game with the saves you want to keep. (PC/Mobile)
  
• Step 2. Logout the game with the saves you DON'T want to keep. (PC/Mobile)
  
• Step 2a. For added safety you can also choose to do re-install the game/clear app data. (C:>Users>Username>AppData>Local>Steam>MuseDash)
  (Remember to turn off steam cloud sync first!)
  
• Step 3. Log back in to sync the remaining autosave to the platform you chose at Step 2.

The logic is to set the save you want to keep as a priority and overwrite it to other platforms.
If Google is your only pick then the safest way is to always logout when you're done with a platform and wanted login to another platform.

So the reason behind this guide is because I had first hand experience when I lost my save data. And after I did some searching online hoping to find a solution that's when I found out a lot of players have had experienced the same problem like me. So for ease of access, I bundle the useful info into this somewhat short guide hoping it will be useful for others.

• Muse Dash Q&A section
  
• Steam Discussions
  
• Reddit r/MuseDash