vito/app/Web/Pages/Settings/Projects/Widgets/AddUser.php

<?php

namespace App\Web\Pages\Settings\Projects\Widgets;

use App\Models\Project;
use App\Models\User;
use Filament\Forms\Components\Actions\Action;
use Filament\Forms\Components\Section;
use Filament\Forms\Components\Select;
use Filament\Forms\Concerns\InteractsWithForms;
use Filament\Forms\Contracts\HasForms;
use Filament\Notifications\Notification;
use Filament\Widgets\Widget;

class AddUser extends Widget implements HasForms
{
    use InteractsWithForms;

    protected static string $view = 'components.form';

    public Project $project;

    public ?int $user;

    public function mount(Project $project): void
    {
        $this->project = $project;
    }

    public function getFormSchema(): array
    {
        return [
            Section::make()
                ->heading('Add User')
                ->schema([
                    Select::make('user')
                        ->name('user')
                        ->options(fn () => User::query()->pluck('name', 'id'))
                        ->searchable()
                        ->rules(\App\Actions\Projects\AddUser::rules($this->project)['user']),
                ])
                ->footerActions([
                    Action::make('add')
                        ->label('Add')
                        ->action(fn () => $this->submit()),
                ]),
        ];
    }

    public function submit(): void
    {
        $this->authorize('update', $this->project);

        $this->validate();

        app(\App\Actions\Projects\AddUser::class)
            ->add($this->project, [
                'user' => $this->user,
            ]);

        Notification::make()
            ->title('User added!')
            ->success()
            ->send();

        $this->user = null;
    }

    public function updated(): void
    {
        $this->dispatch('userAdded');
    }
}