Answers for "problem 1 - root composer.json requires laravel/ui 2.4 -> satisfiable by laravel/ui[v2.4.0]. - laravel/ui v2.4.0 requires php ^7.2.5 -> your php version (8.0.3) does not satisfy that requirement."

- root composer.json requires php ^7.1.3 but your php version (8.0.3) does not satisfy that requirement.

It's becouse in your project in composer.json file you have:

"require": {
    "php": ">=7.3",
    .....
},
Try to update this requirement to:

"require": {
    "php": "^7.3|^8.0",
    .....
},