My suggestion is to embed a function to JabRef, which will go through all the keywords inserted in the General tab, keywords field and convert them to lowercase or uppercase, therefore, there will be no unnecessary difference between “Artificial Intelligence” and “artificial intelligence” for example.
this is already possible through the Cleanup operations.
Quality → Cleanup entries
Add the field “keyword” to the field names and then choose one of the Uppercase, lowercase or Capitalize formatter.
A list of formatters is explained here Save actions - JabRef