Right, I forgot about the difference in engine versions. The game is essentially running on version 3.3 of the Godot engine, whereas the most recent version is 4.7.1, which includes a significant overhaul of the string variable functions. This is the relevant document for the game's string functions: https://docs.godotengine.org/en/3.3/classes/class_string.html. The string functions are still somewhat crude, so you will probably want to use the clunky #2 approach for most things. Alternatively you could use dictionaries to convert string keys into boolean values or integers, though it's really just pushing the bulk and work to somewhere else.
Godot is the game engine. GDScript is simply an abbreviation for Godot Script. Godot can run on other languages than GDScript, such as C#.
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Oooh, that's a useful doc; thanks!
Oddly enough, despite it being less efficient than later versions, I do kinda appreciate having a version set in a given form. Far too many things moving faster than my workflow can account for these days, so it's nice to have a thing where I can learn it at my own pace and not have to keep up with changes.