Here is a quick video about the subject and what's wrong with this Feed Through Lugs.
What I found out is that the Feed Through Lugs does not work with Circuit Naming. And for some reason, the Icons of the Breaker and Feed Through Lugs are missing in Revit 2023...

Here is the Revit Mep Forum about the subject: https://forums.autodesk.com/t5/revit-mep-forum/feed-through-lugs-is-useless-revit-electrical/td-p/11...
Here is another Revit Idea about Spare/Space Circuit Naming problem.
Add Shared Parameter to 'Electrical Spare/Space Circuits' Category: https://forums.autodesk.com/t5/revit-ideas/add-shared-parameter-to-electrical-spare-space-circuits-c...