Sidebar folder shortcuts all disappeared after update
Try Finder prefs > Sidebar -  Cmd ⌘   ,  - they may just have become unchecked…



Any that are still missing after that - previous customer entries etc, can be restored by selecting the appropriate drive/folder/app in any Finder window &amp; hitting  Opt ⌥   Ctrl ⌃   Cmd ⌘   /  or File Menu > Add to Sidebar

Perhaps Time Machine would have an older version?
The prefs are at /Library/Preferences/com.apple.sidebarlists.plist
If you navigate there then enter Time Machine, it may have an older version you could recover