Assuming you are using the Windows version, it would be inside of the main folder, CiC 0.48.6. The file you need to run the game is simply called "game.exe".
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Ah okay, it's different on the web version. You'll need to run the index.html file. If it asks you what to open it with, you'll want to select a web browser. You will also need to configure your browser to allow it to play RPG Maker MV games, as it generally won't work by default. This link should tell you how to do that. https://www.reddit.com/r/RPGMaker/comments/dqvdqo/fix_error_failed_to_load_dataa...
And if you're curious about the Mac version, it probably doesn't work because your Mac is too new. RPG Maker MV support of Mac ended in the middle of me making the game, but I still upload the Mac version because it will still work on older machines.