Composer detected issues in your platform: Your Composer dependencies require a PHP version ">= 7.3.0"
Solution:
1. add this line in config object of composer.json file
"platform-check": false
2. open Terminal and run php artisan config:cache
3. then run composer dump-autoload ## Refererence from : stackorverflow.com
3. then run composer dump-autoload ## Refererence from : stackorverflow.com