Option 1
use Arcgis PRO attribute editor
You can't run SQL statement in Arcgis Pro, pretty much you will have to manually populate index table, it is time consuming jobs.
I can do a small test here, but will not use this method for the whole index, too much work.
Option 2
Use enterprise Geodatabase, you can just use SQL management studio to run SQL select distinct keywords.
Or use SQL group by to get the unique keywords.
Each time you get unique keyword from 1 layer 1 field, then records layer name and field name populate into index table.
There are lots of work here, don't do it manually, instead, should use SQL statement to semi-automatic extract keywords also populate into index table.
option 3
Automatic index generation, each new record added to all in one layer, a new index table should be generated automatically.
Should use python script or SQL statement to automatically read new record then automatically insert new rows into index table.