I remember what.
At Version 5.4.0, Katalon Studio introduced “Execution Profile”. See the release note.
https://docs.katalon.com/katalon-studio/new/version-540.html#test-execution
Prior to 5.4.0, all we had was the term “Global Variable” and we did not have the term “Execution Profile”. In other words, we had a single Execution Profile, what we call “default” now, but we could not have multiple sets of global variables. In order to support multiple sets of global variables, Katalon Studio significantly changed the code format of <projectDir>/Libs/internal/GlobalVariable.groovy. I am quite sure that the following code fragment newly appeared at that time.
$FOO = selectedVariables["$FOO"]
Why do I remember this so clearly? Well, the following post of mine at March 2018 motivated, I believe, Katalon team to introduce the “Execution Profile” concept: multiple sets of global variables.