Magent 2.3.4 Installation error

Question

I was do setup the magento 2.3.4 version in Php 7.3 version
But Frontend throw error

Fatal error: Composer detected issues in your platform: Your Composer dependencies require a PHP version ">= 7.4.0". You are running 7.3.33-1+ubuntu20.04.1+deb.sury.org+1. in /magentoroot/vendor/composer/platform_check.php on line 24

After i runed below commands :
composer install, composer update and composer -v
it is thow error

Fatal error: Uncaught Error: Call to undefined function Composer\Json\json_decode() in /usr/share/php/Composer/Json/JsonFile.php:169

How to solve this problem ?

Answer 1

Update Project or global composer.json file under config section :

{
    "config": {

        "platform-check": false
    }
}

After that Run commands :

composer update
composer dump

After that Run the magento commands for setup upgrade, compile and deploy commands.

Hopefully It will resolve.