Never mind, I figured it out!
This is one way to fix the Google Search Console breadcrumb issue in Wordpress.
Here's what worked:
RewriteCond %{QUERY_STRING} ^cat=-1$ [NC]
RewriteRule ^ - [R=404]
I want to have requests to this url result in a 404 response, via the Rewrite Rules setting for the virtual host in the OLS web console:
https://www.example.com/?cat=-1
I have a 404 rule working for another page, but this one has been stubborn to find the right rule expression.
I've tried this...