Laravel7项目Composer dump-autoload报错：PHP版本切换后仍异常

• 项目背景：Laravel 7部署在虚拟主机子目录，此前运行正常；主机商将全局PHP版本升级至v8.1.12后，执行composer dump-autoload出现报错。
• 当前状态：已将项目对应的PHP版本切换回7.4甚至7.3，但执行composer update时，在Generating optimized autoload files步骤会触发以下弃用通知：

Deprecation Notice: Return type of  Illuminate\Container\Container::offsetExists($key) should either be compatible with ArrayAccess::offsetExists(mixed $offset): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in  /home1/rootfolder/public_html/projectfolder/vendor/laravel/framework/src/Illuminate/Container/Container.php:1270 
Deprecation Notice: Return type of  Illuminate\Container\Container::offsetGet($key) should either be compatible with ArrayAccess::offsetGet(mixed $offset): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /home1/rootfolder/public_html/projectfolder/vendor/laravel/framework/src/Illuminate/Container/Container.php:1281 
Deprecation Notice: Return type of Illuminate\Container\Container::offsetSet($key, $value) should either be compatible with ArrayAccess::offsetSet(mixed $offset, mixed $value): void, or the  [\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /home1/rootfolder/public_html/projectfolder/vendor/laravel/framework/src/Illuminate/Container/Container.php:1293 
Deprecation Notice: Return type of Illuminate\Container\Container::offsetUnset($key) should either be compatible with ArrayAccess::offsetUnset(mixed $offset): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /home1/rootfolder/public_html/projectfolder/vendor/laravel/framework/src/Illuminate/Container/Container.php:1306 
> @php artisan package:discover --ansi

• 环境矛盾：本地执行php --version显示当前PHP版本为7.3.33，但Composer似乎仍在使用主机根目录的PHP 8.1.12版本。
• 已尝试方案：修改composer.json中的PHP版本约束、执行composer update/composer install/composer self-update、清除Composer缓存、联系主机技术支持，均未解决问题。
• 需求：项目依赖暂未适配Laravel 8/9，不想升级整个项目，寻求可行的技术解决方案。

内容的提问来源于stack exchange，提问作者Urget