Quick Apple Script to sort Apple Music Favorites based on an export from a different service

gistfile1.txt

tell application "Music"
    with timeout of 7200 seconds
        -- Detect which property to use
        set useProperty to missing value
        set testTrack to track 1 of playlist 1
        
        try
            set favorited of testTrack to (favorited of testTrack)
            set useProperty to "favorited"
        end try
        
        if useProperty is missing value then
            try
                set loved of testTrack to (loved of testTrack)
                set useProperty to "loved"
            end try
        end if
        
        if useProperty is missing value then
            display dialog "Could not determine favourite property. Aborting." buttons {"OK"} default button 1
            return
        end if
        
        display dialog "Using property: " & useProperty buttons {"OK"} default button 1

        -- Find playlist
        set thePlaylist to missing value
        repeat with p in (get every playlist)
            if name of p is "Spotify Liked" then
                set thePlaylist to p
                exit repeat
            end if
        end repeat

        if thePlaylist is missing value then
            display dialog "Playlist 'Spotify Liked' not found!" buttons {"OK"} default button 1
            return
        end if

        set trackIDs to (get database ID of every track of thePlaylist)
        set trackCount to count of trackIDs
        display dialog "Found " & trackCount & " tracks. Starting..." buttons {"OK"} default button 1

        set successCount to 0
        set failCount to 0

        repeat with i from trackCount to 1 by -1
            set aID to item i of trackIDs
            try
                set aTrack to (first track whose database ID is aID)
                if useProperty is "favorited" then
                    set favorited of aTrack to true
                else
                    set loved of aTrack to true
                end if
                set successCount to successCount + 1
            on error
                set failCount to failCount + 1
            end try
            if (i mod 50) is 0 then delay 1
        end repeat

        display dialog "Done! Favourited: " & successCount & " | Failed: " & failCount buttons {"OK"} default button 1
    end timeout
end tell

Why loved vs favorited matters
Apple Music exposes two different AppleScript properties for the same "heart/favourite" feature depending on your system region:

US English systems use loved (corresponding to the "Love" button in the UI)
UK, Australian, and other English systems use favorited (corresponding to the "Favourite" button)

Using the wrong property doesn't throw an obvious error — it either silently does nothing or returns a generic access error like Can't set «constant eClSkMat» to false. Access not allowed., which is extremely misleading as it implies a permissions issue rather than a naming mismatch. The same likely applies to non-English systems where the button has a different localised name entirely.
This script auto-detects which property works on your system before proceeding.
If the script fails:

Done! Favourited: 0 | Failed: X → The detection passed but tracks are still unwritable. Check that the tracks are actually in your Library (not just a shared/imported playlist). Cloud-only tracks that haven't been added to your library may be read-only.
"Could not determine favourite property" → Neither loved nor favorited works on your system. You may be on a non-English locale — open Script Editor, manually try set loved of track 1 of playlist 1 to true and set favorited of track 1 of playlist 1 to true to find which property name works, then hardcode it.
"Playlist 'Spotify Liked' not found" → The playlist name doesn't match exactly. Open Music, check the exact name and update the script accordingly.