You can use innoextract to extract RCT2 GOG installer. Look at: https://constexpr.org/innoextract/#gog
On mac you basically use
brew install innoextract
innoextract -g -d [outputDirectory] [exeFile]
and you can find game files in [outputDirectory]/app. That's the directory I pointed RCT2 to and it worked for me just right now :)