Katalon Studio uses Groovy version 2.4.x.
In Groovy version 2.4.x, the do {} while … loop is not supported. You can check the language document at
https://docs.groovy-lang.org/docs/groovy-2.4.21/html/documentation/#_looping_structures
The do {} while … loop was added at the version 3.0 of Groovy language
https://docs.groovy-lang.org/docs/groovy-3.0.0/html/documentation/#_do_while_loop
However, as far as I am aware, Katalon team has no intention to move to Groovy v3.0 in Katalon Studio.
I don’t think they will do it. Katalon team has ever tried it but encountered difficulties; they abandoned their intent. See the following post: