MacOS – Finder sidebar icons showing as circles for disks

This isn't an answer but it does add some information. The value associated with the com.apple.LSSharedFileList.TemplateSystemSelector key, 1935819875, is a decimal representation of the file type. In hex, it is 0x73624463, which are the ascii letters 'sbDc'. This file type is described in /System/Library/CoreServices/CoreTypes.bundle/Contents/Info.plist. This is a binary plist that you can convert to xml using plutil -convert xml1 -o Info.plist.xml Info.plist. Looking in the Info.plist.xml file, you can see a dictionary at the top level. Inside this there is a key "CFBundleDocumentTypes" and an array of dictionaries as its value. In this array is a dictionary that contains the following:

<dict>
    <key>CFBundleTypeIconFile</key>
    <string>SidebarDocumentsFolder.icns</string>
    <key>CFBundleTypeName</key>
    <string>Sidebar Documents Folder Icon</string>
    <key>CFBundleTypeOSTypes</key>
    <array>
        <string>sbDc</string>
    </array>
    <key>CFBundleTypeRole</key>
    <string>None</string>
    <key>LSTypeIsPackage</key>
    <false/>
    <key>NSPersistentStoreTypeKey</key>
    <string>Binary</string>
</dict>

An interesting key/value pair in this dictionary is CFBundleTypeIconFile: SidebarDocumentsFolder.icns. This file can be found at /System/Library/CoreServices/CoreTypes.bundle/Contents/Resources/SidebarDocumentsFolder.icns and it contains the icons used for document folders.

I would think that changing the com.apple.LSSharedFileList.TemplateSystemSelector value to a different value, or updating the dictionary for 'sbDc' to refer to a different icns file would get you on your way to having custom icons.

try this in Terminal

mkdir ${TMPDIR}/com.apple.IconServices

This recreates the com.apple.IconServices directory, which apparently gets itself deleted from time to time.