what do I use to unpack the file?
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The version for Linux is stored in a .zip archive that you can unpack with right-click ->"Extract here" on Linux. If you want to unpack .7z archives on Linux, you can install 7zip on Linux with such a sequence of commands, and then it will be available for extraction with right-click menu, too:
sudo add-apt-repository universe
sudo apt update
sudo apt install p7zip-full p7zip-rar
It seems that your OS is missing the integration of the Archive Manager app into GUI ( https://askubuntu.com/questions/659778/cant-extract-archives-in-gui-anymore ), and you can fix this by running this command:
sudo apt-get install file-roller
I suggest installing the 7zip packages mentioned above afterward if you want to unpack .7z archives, too.