I'd be interested in your solution as there are several RPGM games I'd like to try if it were possible to run them. I didn't even know there were any potential workarounds, short of emulating Windows or running an old Mac. And I think most Mac players know that RPGMaker doesn't actually support them anymore, so we just kinda sigh and move on to another game.
The one solution that I've had confirmed working was only confirmed by one person, but I've suggested others try it and they didn't come back saying it didn't work, so that might be the best I've got.
Trying to be as concise as possible; (this isn't something I made, so use your best judgment) download this and extract it, then find "package.json" and rename it to the game name.
Once that's done, go to Game.app/Contents/Resources/app.nw/, then copy these files from my game's files: audio, css, data,
fonts, icon,
img,
js,
locales,
movies,
switshader,
credits.html,
FOSSILindex.html,
index.html,
package.json, README.txt.
Once those are copied over, the app should launch. This may require downloading the Windows version of the game instead of the Mac version; I can't test it for myself so I'm a little unclear on that. Definitely let me know if it works for you, though. The next best suggestion I have is to use something like Wine, but I've had a bunch of people say it doesn't work for them.
So I got it figured out and the game does work now. I'm afraid the instructions you were given are incorrect, though. Here's what I did. Download both the Mac version of the game and the zip file you linked on Google Drive. When you open both you'll have two apps, both named "Game.app". View Package contents on both apps in separate windows, then navigate to the /Contents/Resources/app.nw/ in both. The Game.app from Google Drive will have nothing in this folder, while the Game.app from the Mac game package will have all the game contents. Copy the entire contents of the Mac Game.app over to the Google Drive Game.app and close both windows. Then replace the Game.app file in the Mac game folder with the newly updated one from Google Drive. It should now launch properly. Note, that the Game.app file must be moved into the folder where the original Game. app file was or it will not launch. If you'd like, I can take screenshots of the process and send them to you.
I'm glad you got it to work for you!
Feel free to add screenshots to your post for posterity if you think it'd be helpful. It's hard to put an official guide together when all the solutions I have are only confirmed to work for one or two people, but it'll be good to have your steps around to see if they work for others.
Speaking of others - if you happen to be reading this comment chain trying to figure out how to get the Mac version working and this method works for you, drop mephits an upvote. It's the easiest way to let me know the method worked for you as well.