How to find several photos at once in the LR library?

FYI- From my notes: Adding to the good replies above.

To find a large selection of images from a text list you need to follow a set procedure-

Lightroom-Classic needs access to all images that may be in the list- Click on ‘All Photographs’ in the Library, Catalog  panel- left of screen, or select the folder where all the searched images are known to exist. ***Note: This method does not work if you have filenames containing spaces! (Under-scores are OK)

1) Edit your list in a text editor (MS-Word or Notepad, etc) so that the list of file-names are separated by commas (One space following the comma separating the filenames is ok.) and delete all Paragraph markers. (This is the time-consuming part!)

2) Select this list by high-lighting only the file-name text characters with the mouse. (No paragraph markers, no quote marks, no tabs )

3) Select and COPY the text list to the clip-board. [CTRL-C] or [Right-click > Copy]

4) In Lightroom-Classic:  [Menu > Library > Find],   [CTRL+F]

or Click "Text" on the Library filter bar, and set it to- Filename / Contains.

Be sure that you've selected Filename “Contains” in the Library filter bar.

If there is a space imbedded in any of the filenames this approach won't work, (The space following the comma separating the filenames is ok.)

5) Click in the Search box and paste the list [CTRL+V]  or [Right-click > Paste]

 You will see thumbnails of all the listed images by Filename. 

6) From this Grid view you can add these images to a Standard Collection by-

Select all [CTRL+A], Click the Collection Panel [+], Check ‘add selected images’.

Hard to see from your screenshot, but what probably happens is that Lightroom searches for images that contain all these names rather than any of these names.

Hard to say if you don't show us a screen capture (please use the "Insert Photos" icon to include your screen capture in your reply, do NOT attach files)

This works for me. I select "All Photographs", then in the Filter Bar, I select Filename and I select Contains and then type in the desired file names.