Easy to do...in the Library module under the Metadata tab scroll down to the bottom and click on Purge Unused Keywords.
Mine says "Purge extras" a. Hit the drop down and a grayed sign says no extras. I have Win 11 and the very latest Lightroom version if that make any difference
I can’t recall how but you can export your keyword list to a text file which you can edit with a word processor and then re install. The list has indentations to show hierarchy.
Mine says "Purge extras" a. Hit the drop down and a grayed sign says no extras. I have Win 11 and the very latest Lightroom version if that make any difference