Of course, someone who is not logged-in must be able to access the login page and the lost password page.  So here's the code I'm using now, which doesn't override a request for the "lostpassword" template.

<?php
// Exit if accessed directly
if( ! defined( 'ABSPATH' ) ) exit;

if (!is_user_logged_in()) {
    if ($this->current_object != 'lostpassword') {
        $this->current_object = 'login';
    }
    $this->settings->components = false;
    $this->settings->components = false;
    $this->settings->components = false;
}

include $this->tpl->template_dir . '/index.php';

So, I create a "wpforo" folder in my own WP theme directory.  I add "index.php" to the "wpforo" folder, with this code, which overrides the WPF theme "index.php" file.

<?php
// Exit if accessed directly
if( ! defined( 'ABSPATH' ) ) exit;


if (!is_user_logged_in()) {
    $this->current_object = 'login';
    $this->settings->components = false;
    $this->settings->components = false;
    $this->settings->components = false;
}


include $this->tpl->template_dir . '/index.php';

• Create a wpforo directory in my theme folder
• Copy \wp-content\plugins\wpforo\themes\2022\index.php into my wpforo directory
• Add this code near the top of the copied file:

if (!is_user_logged_in()) {
    include __DIR__.'/my-login.php';
    return;
}

• Copy \wp-content\plugins\wpforo\themes\2022\index.php into my wpforo directory again, but naming it "my-login.php"
• Strip down "my-login.php" so that the only template it invokes is wpforo_template('login'), and remove the forum header / footer blocks.

I could have just made more changes to the original copy of index.php, but I wanted to keep the modifications there to a minimum.  It will be easier to copy again if I ever need to.

Thanks again.  I'm currently testing a solution using a custom theme per the docs at https://wpforo.com/docs/wpforo-v2/forum-themes/theme-customization/

By copying index.php into my own theme folder, I can add conditional logic that is used to hide some elements, and force the login form to be displayed, if the user is logged out.

OK, I appreciate the warning, although I'm not 100% sure what the problems will be. 

The problems will be that you try to control a page that wpForo controls. We have seen that happen here and the guys couldn't tell from where it was coming. wpForo or the block.

Anyways, you can try.

OK, I appreciate the warning, although I'm not 100% sure what the problems will be. 

My requirement is this - if someone is not logged in, I don't want them to be aware that there is a forum, or to be able to access any forum pages / see member profiles etc.

The forum is exclusively for logged-in users.

What suggestions do you have for how this can be done?

Nope, this is an open invitation for trouble.

Thanks for that, and for the useful links.

My understanding is that I need to set "No Access" for "Guest" on every forum, and there is no single global setting for "Guests", to disallow all forums.  I can see that this would work.

I think however I will try protecting the "/community" page, so that it can only be reached by logged-in users.

You can restrict accessfor guests by setting 'No Access' for 'Guest' usergroup. 

Please check out this FAQ to better understand the forum access and user group connections: https://wpforo.com/community/faq/wordpress-user-roles-wpforo-usergroups-and-forum-accesses/#post-39664

The solution provided by another community member should also be helpful for you: https://wpforo.com/community/how-to-and-troubleshooting-2/how-to-hide-forum-for-guests/#post-103677

There's one thing I need a bit of help with, though - I only want logged-in users to be able to access the forums.  If a "Guest" tries to access the forum page ("/community"), they must see nothing at all, or maybe just a login page.

I can't see an easy option to do this in the plugin settings.  I understand that Accesses are used to manage permissions on each forum, rather than for all forums.

My alternative is to protect the "community" page itself, so that only logged-in users can see it.  Perhaps that's what I have to do - or is there a plugin setting that will do it?