mb_user_profile_register autocomplete="new-password" ?

Hi Adam,

Thank you for getting in touch.

If you want to add any attribute to a field input, please follow this documentation https://docs.metabox.io/custom-attributes/.

Then use filter rwmb_profile_register_fields to customize/modify the user register fields.

Sample code:

function add_more_registration_fields( $fields ) {
        $fields = [
            'password'  => [
                'name'     => __( 'Password', 'mb-user-profile' ),
                'id'       => 'user_pass',
                'type'     => 'password',
                'required' => true,
                'desc'     => '<span id="password-strength" class="rwmb-password-strength"></span>',
                'attributes' => [
                    'autocomplete' => 'new-password'
                ]
            ],
            'username'  => [
                'name'     => __( 'Username', 'mb-user-profile' ),
                'id'       => 'user_login',
                'type'     => 'text',
                'required' => true,
            ],
            'email'     => [
                'name'     => __( 'Email', 'mb-user-profile' ),
                'id'       => 'user_email',
                'type'     => 'email',
                'required' => true,
            ],           
            'password2' => [
                'name'     => __( 'Confirm Password', 'mb-user-profile' ),
                'id'       => 'user_pass2',
                'type'     => 'password',
                'required' => true,
            ],
            // ... add more fields here
        ];
        return $fields;
    }
add_filter( 'rwmb_profile_register_fields',  'add_more_registration_fields' );

Refer to the topic
https://support.metabox.io/topic/registration-username-as-email-duplicated-fields-avatar-visibility-issue/
https://support.metabox.io/topic/sort-the-username-and-email-fields/