This is an example of how one could create a custom type for roles to add in a User form

messages.fr.yml

security:
    roles_label: "Permissions"
    roles:
        ROLE_SUPER_ADMIN: "Super Admin"
        ROLE_ADMIN: "Administration"
        ROLE_MONITOR: "Monitoring"
        ROLE_FLEET: "Gestion du parc"
        ROLE_ADMIN_USER: "Gestion des utilisateurs"
        # ...

RolesType.php

<?php

namespace AdminBundle\Form;


use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\ChoiceType;
use Symfony\Component\OptionsResolver\OptionsResolver;
use Symfony\Component\Security\Core\Authorization\AuthorizationChecker;
use Symfony\Component\Security\Core\Role\Role;
use Symfony\Component\Security\Core\Role\RoleHierarchy;

class RolesType extends AbstractType
{
    protected $reachableRoles;
    protected $roleChoices;
    private $transPrefix = 'security.roles.';


    public function __construct(RoleHierarchy $roleHierarchy, AuthorizationChecker $authorizationChecker)
    {
        $superAdminRole = 'ROLE_SUPER_ADMIN';
        $currentPermissions = array(new Role($superAdminRole));
        $this->reachableRoles = $roleHierarchy->getReachableRoles($currentPermissions);
        $this->roleChoices = $this->getRoleChoices();
        if (!$authorizationChecker->isGranted($superAdminRole)) {
            unset($this->roleChoices[$this->transPrefix.$superAdminRole]);
        }
    }


    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults(array(
            'label' => 'security.role_labels',
            'choices' => $this->roleChoices,
            'choice_translation_domain' => true,
            'expanded' => true,
            'multiple' => true,
        ));
    }


    private function getRoleChoices()
    {
        $roles = array();
        /** @var Role $role**/
        foreach ($this->reachableRoles as $role) {
            $roles[$this->transPrefix.$role->getRole()] = $role->getRole();
        }

        return $roles;
    }


    public function getParent()
    {
        return ChoiceType::class;
    }
}

security.yml

security:
    role_hierarchy:
        ROLE_SUPER_ADMIN:
            - ROLE_ADMIN_USER
            - ROLE_ADMIN
            - ROLE_MONITOR
            - ROLE_FLEET
        ROLE_ADMIN_USER:
            - ROLE_ADMIN
        # ...

services.yml

services:
    admin.form.user_roles_type:
        class: AdminBundle\Form\RolesType
        arguments: ['@security.role_hierarchy', '@security.authorization_checker']
        tags:
            - { name: form.type}

Here I'm simply removing the ROLE_SUPER_ADMIN for non super admin users but the selectable choices could be based on the granted roles.

Thanks for sharing this 👍