mandant-crm/backend/app/Modules/User/Policies/UserPolicy.php

<?php

namespace App\Modules\User\Policies;

use App\Models\User;

class UserPolicy
{
    public function viewAny(User $user): bool
    {
        return $user->isAdmin();
    }

    public function create(User $user): bool
    {
        return $user->isAdmin();
    }

    public function update(User $user, User $target): bool
    {
        return $user->isAdmin();
    }

    public function delete(User $user, User $target): bool
    {
        if (! $user->isAdmin()) {
            return false;
        }
        if ($target->isAdmin() && User::where('role', 'admin')->count() <= 1) {
            return false;
        }
        return true;
    }
}