How do I create an album in photos that includes photos only without people?

Do you mean no people at all, or no people identified as face names by Photos?

If the latter, I can get close to it. I have some Keywords that I use to eliminate identified faces that are not people I know or have named. These include StrangersOnly and StrangersInc[luded], which identify pictures that include identified faces that I have not named.

If you put these into a Smart Album like this (where the third condition is empty):

You get an album that contains no identified people. It still contains pictures that include people but nothing that Photos has identified as a face, so its mainly without people at all.

Stephen

I can't find a way to do it automatically.

The "Person does not include" rule is brilliant, Stephen! I have always been doing it with "Person is not ", but it does only find unnamed faces.