Problem 1 - Root composer.json requires laravel/ui 2.4 -> satisfiable by laravel/ui[v2.4.0]. code example
Example 1: composer require laravel/ui laravel 7
composer require laravel/ui:^2.4
Example 2: composer require laravel/ui laravel 7
// Generate basic scaffolding...
php artisan ui bootstrap
php artisan ui vue
php artisan ui react
// Generate login / registration scaffolding...
php artisan ui bootstrap --auth
php artisan ui vue --auth
php artisan ui react --auth