Open the affected Finder window and choose View → Show Sidebar. If the command is grayed out, choose View → Show Toolbar first. If you can see the sidebar and only some items are missing, expand the section or check Finder settings.
01The entire left side is missing
Section linkClick the affected Finder window and open the View menu. Choose Show Toolbar first if Show Sidebar is dimmed, then choose Show Sidebar. When the sidebar is visible but narrow, drag the divider to the right to make the names easier to read.
02Favorites or Locations looks empty
Section linkMove the pointer over the section name and click the arrow that appears. If a default item such as Downloads is still missing, open Finder → Settings → Sidebar and select the checkbox for that item. If Favorites is missing entirely, select an item from that group in the settings.
03Put a custom shortcut back
Section linkFind the original folder and drag it into Favorites. For a file or an app, hold Command while dragging it into Favorites. These shortcuts point to the original items, so adding a folder to the sidebar leaves it where it is.
04Check whether the shortcut opens the right folder
Section linkClick the restored item. If you are restoring a shortcut to Downloads, for example, you should see the contents of Downloads in the main Finder pane. If the missing item was a custom shortcut, find the original in Finder before adding it again.