charus
I know how to install theme but just wondering where you get MAMP version 5.6 as in the official site, the latest one is 5.5: https://www.mamp.info/en/downloads/
For the error, I guess you're using Quickstart package file to install via admin panel. If you already have a WP site, you need to select theme package to install via admin panel.
Installing quickstart package would be the same as default WP package but with sample data of theme.
Kindly check again.