With the incredible help of my fellow Champion @yosiasz here is the JSONata you can use to separate the string:
UQL with JSONata (as used in Infinity plugin) is
parse-json
| jsonata "($map($, function($v) {{'RollNameDigits': $substringBefore($v.`Roll-Name`,'-'),'RollNameLetters': $substringAfter($v.`Roll-Name`,'-')}}))"