Composer Laravel9 PHP8アップデートについて

前提

現在PHP 7.4.30　Laravel6.20.2　です。
composer installでPHP8とLaravel９のアップデートを試していますがうまくいきません。

エラーメッセージ

No composer.lock file present. Updating dependencies to latest instead of installing from lock file. See https://getcomposer.org/install for more information.
Loading composer repositories with package information
Updating dependencies
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - illuminate/support[v5.6.0, ..., v5.8.36] require php ^7.1.3 -> your php version (8.0.22; overridden via config.platform, same as actual) does not satisfy that requirement.
    - illuminate/support[v6.0.0, ..., v6.19.1] require php ^7.2 -> your php version (8.0.22; overridden via config.platform, same as actual) does not satisfy that requirement.
    - Root composer.json requires laravel/framework ^9.23.0 -> satisfiable by laravel/framework[v9.23.0].
    - laravel/tinker v1.0.10 requires illuminate/support ~5.1|^6.0 -> satisfiable by illuminate/support[v5.1.1, ..., v5.8.36, v6.0.0, ..., v6.20.44].
    - Only one of these can be installed: illuminate/support[v5.1.1, ..., v5.8.36, v6.0.0, ..., v6.20.44, v7.0.0, ..., v7.30.6, v8.0.0, ..., v8.83.23, v9.0.0, ..., v9.23.0], laravel/framework[v9.23.0]. laravel/framework replaces illuminate/support and thus cannot coexist with it.
    - Root composer.json requires laravel/tinker ^1.0.10 -> satisfiable by laravel/tinker[v1.0.10].

該当のソースコード

composer.json
1{
2    "name": "laravel/laravel",
3    "description": "The Laravel Framework.",
4    "keywords": ["framework", "laravel"],
5    "license": "MIT",
6    "type": "project",
7    "config": {
8        "preferred-install": "dist",
9        "sort-packages": true,
10        "platform": {
11            "php": "8.0.22"
12        }
13    },
14    "require": {
15        "php": ">=8.0.22",
16        "fideloper/proxy": "^4.4",
17        "laravel/framework": "^9.23.0",
18        "laravel/tinker": "^1.0.10",
19        "predis/predis": "^1.1"
20    },
21    "require-dev": {
22        "filp/whoops": "~2.0",
23        "fzaninotto/faker": "~1.4",
24        "laravel/dusk": "^6.11",
25        "mockery/mockery": "0.9.*",
26        "phpunit/phpunit": "^8.0",
27        "symfony/css-selector": "3.1.*",
28        "symfony/dom-crawler": "3.1.*"
29    },
30    "autoload": {
31        "classmap": [
32            "database"
33        ],
34        "psr-4": {
35            "App\\": "app/"
36        }
37    },
38    "autoload-dev": {
39        "psr-4": {
40            "Tests\\": "tests/"
41        }
42    },
43    "scripts": {
44        "post-root-package-install": [
45            "php -r \"file_exists('.env') || copy('.env.example', '.env');\""
46        ],
47        "post-create-project-cmd": [
48            "php artisan key:generate"
49        ],
50        "post-install-cmd": [
51            "Illuminate\\Foundation\\ComposerScripts::postInstall",
52            "php artisan optimize"
53        ],
54        "post-update-cmd": [
55            "Illuminate\\Foundation\\ComposerScripts::postUpdate",
56            "php artisan optimize"
57        ],
58        "post-autoload-dump": [
59            "Illuminate\\Foundation\\ComposerScripts::postAutoloadDump",
60            "@php artisan package:discover"
61        ]
62    },
63    "extra": {
64        "laravel": {
65            "dont-discover": [
66                "laravel/dusk"
67            ]
68        }
69    }
70}
71