I am assuming that the name of the user admin is Phil Taylor

The author is part of the taxonomy in smart search. To confirm this go to the smart seach component and check the content maps. You should see a map entry for Phil Taylor with a parent of author.

(not saying its right or wrong to just explaining how smart search works)

You assume wrong. My admin usernames "name" is also "admin"

"PhilTaylor" exists no where in my database. It's not a users name, alias, or otherwise used at all on the site. It was just a poor illustration of a generic text string. Sorry if it's use deflected from the actual bug.

You can replicate the reported bug by searching with any random text string you like as long as it's a single word without spaces

In that case I can not confirm your findings

Well now Im in the office, so totally different machine in a totally different location, I follow the instructions to the letter in the opening post of this issue and I can still replicate the issue on this iMac too.

(dockerised) mysql 5.7 version just in case that makes a difference.

Video from installing : https://screenshot.phil-taylor.com/4guJmyXp

Enable: Allow empty search

Sorry I missed that part. That is the key to replicating the bug

(IM ASSUMING THIS MEANS: You can search for "")

From memory its related to using the advanced search filters without a search term. But clearly its not working at all

Here is a fix: #31040