Lightroom Classic: How to filter for Images with no Keywords

There are numerous differences between smart collections and filters most people aren't aware of:

1. You can save the search criteria "Keywords are empty" both in smart collections and Library Filter bar presets, so that it only takes a click or two to call up either (depending on how many of each you have and whether you have to scroll the left column):



2. You can always select a filter preset in the right corner of the filmstrip, but you may or may not be able to select the smart collection from the filmstrip's recent sources in the left corner:



3. Both smart collections and filters update what's shown in the grid view and filmstrip continuously in real time as photos are changed.

4. A smart collection searches your entire catalog and shows you all matching photos, including photos hidden in collapsed stacks.  It's possible but not very easy to restrict a smart collection to a particular source (collection or folder) -- it takes several steps most people won't remember.

A filter searches just the current source (collection or folder) and doesn't show photos that are in collapsed stacks. So unlike smart collections, it's easy to restrict a filter to different sources.  But if you want to search your entire catalog, it takes  extra steps -- select All Photographs, expand all stacks, apply the filter.

5. You can't manipulate stacking while viewing a smart collection, but you can while using a filter.

6. You can have different filters for different sources (collections and folders).

7. Smart collections have more criteria and allow for general boolean combinations of And, Or, and Not.  Filters are restricted to a more limited combination of And and Or.

8. Filters let you do exact match of keywords, whereas smart collections don't.  This can cause smart collections to incorrectly search photos with keywords containing multiple words.

Thanks to everyone. I will try them both and see what works best for me.

Thats correct Don, Library filter is almost the same as smart collections. The interest to have such smart collection is that user has continuously the information present without redoing the library  gimmick.
It's only a question choice or depend from the way the user is working.

In Library, you can also filter on Text > Keywords > Are Empty.  This allows selection without a Smart Collection.  

I do exactly the same approach as John
Create a dynamic collection Choosing : as test zone "Key words"  and as rule "are empty"

Just like the way I do look at the dump screen

Create a smart collection and under the criterion Other Metadata you can choose Keywords / Are Empty.

Also in the Library Filter (the 4 columns at the top of grid) you can change a column to Keywords.