This happens in 23.12beta3 (edd38ca0), but I didn’t test earlier versions.
After doing a File / Import… with “Preserve” option for existing notes:
In the above, if you click on “94 new notes imported.” [Show]
then the Browse window appears and displays the 94 notes.
But if you click on “3 notes already present in your collection.” [Show]
then nothing happens.
If the Browse window is not already open, it doesn’t open.
If the Browse window is already open, it continues to show old contents and does not update.
Clicking on Details to expand does display the 94 Added and 3 Skipped notes.