I'll let you kno how it went.

I'm sorry but HTML will not be enabled for phrases. We've added a new hook at the end of the facebook login information. You can edit and add it too. It'll not be removed after the update, because the same code is also added in the new update.

1. Using cPanel File Manager or Plugin Editor and open this file: /wp-content/plugins/wpforo/wpf-includes/class-api.php

2. Find this line:

<span class="wpforo-fb-info-text">
    <?php echo sprintf( wpforo_phrase('When you login first time using Facebook Login button, we collect your account %s information shared by Facebook, based on your privacy settings. We also get your email address to automatically create a forum account for you. Once your account is created, you\'ll be logged-in to this account and you\'ll receive a confirmation email.', false ), $public_profile); ?>
</span>

3. Change to this and save:

<span class="wpforo-fb-info-text">
    <?php echo apply_filters('wpforo_fb_login_privacy_info', sprintf( wpforo_phrase('When you login first time using Facebook Login button, we collect your account %s information shared by Facebook, based on your privacy settings. We also get your email address to automatically create a forum account for you. Once your account is created, you\'ll be logged-in to this account and you\'ll receive a confirmation email.', false ), $public_profile)); ?>
</span>

4. Then open your current active WordPress theme functions.php file and add custom content via the filter hook. Don't use single quotes in the $add_text value. Change it and add any HTML code you want:

function wpforo_append_html_to_facebook_login_info( $text ){
    $add_text = '<br><a href="https://example.com/community/?foro=page&view=privacy">link</a>';
    return $text.$add_text;
}
add_filter('wpforo_fb_login_privacy_info', 'wpforo_append_html_to_facebook_login_info', 10);

How to Easily Add Custom Code in WordPress (without Breaking Your Site): https://www.wpbeginner.com/plugins/how-to-easily-add-custom-code-in-wordpress-without-breaking-your-site/

Under Forum > Phrases > phrase number 459

It does allow the shortcode %s and creates a link from that. But just plain html it strips.

Please let me know, where did you inset it?

<a href="https://example.com/community/?foro=page&view=privacy">link</a>

it gets stripped.

Here are the URLs for direct access them:

https://example.com/community/?foro=page&view=privacy
https://example.com/community/?foro=page&view=rules

Change the example.com to your website domain and change the /community/ if your forum base URL is different.

I did set those, but when logging in with Facebook, those are being ignored and no longer mandatory.  It doesn't matter if one checks those boxes or not, the Facebook registration/login still functions.

That's why I though, maybe there is a shortcode I can add to the Facebook text so that it at least contains a link to the privacy policy and rules. I tried adding a link with some basic html but that get's stripped out.

I mean something like this %s which is used to create a link like this: public_profile which in turn links to https://developers.facebook.com/docs/permissions/reference#reference-public_profile

I'll suggest you go to the Dashboard > Forums > Tools > Privacy & Rules admin page, fin and check the "Checkbox: I Agree to Forum Privacy Policy" and "Checkbox: I Accept Forum Rules" options. Screenshot below: https://www.screencast.com/t/k8cwdB9MqbC

is there a shortcode that i can use to link to the forum rules and the forum privacy rules? That way i can add those to the Facebook registering/login text.