when I try to run a server on mamp i get the error message: "Composer detected issues in your platform: Your Composer dependencies require a PHP version ">= 8.1.0". You are running 8.0.8".
You don't change package dependencies, that's the responsibility of the package maintainer. Either see if there is another version available that requires the same or lower version of PHP than you have installed in your environment or install the required PHP version.
It appears that MAMP Pro has support for PHP 8.1 although this question seems to have a solution without requiring the Pro version.