Messages to Post navigation & My Spaces URL for primary menu

They don’t support dynamic url tokens. However it’s possible via code snippet.

Amazing! Thank you! Jesse Benjamin 

Patricia Montagno this is a quick fix/solution, I will try to code something better later and may try to expand it further.  

create the menu link, set visibility to "Logged in Only". Then in the url add only this:

{user_url}/spaces

Add this code snippet using whatever code snippet plugin you prefer.

<?php
/**** Usage in FCom Menu URL field: {user_url}/spaces ****/

if (!defined('ABSPATH')) {
    exit;
}

add_filter('fluent_community/main_menu_items', function ($items, $scope) {

    if (!is_user_logged_in() || empty($items) || !is_array($items)) {
        return $items;
    }

    if (!class_exists('\FluentCommunity\App\Services\Helper')) {
        return $items;
    }

    $Helper = '\FluentCommunity\App\Services\Helper';

    // --- Resolve FC username (xProfile preferred) with WP fallback ---
    $username = '';
    try {
        $userModel = $Helper::getCurrentUser();
        if ($userModel) {
            $xprofile = $userModel->syncXProfile(false);
            if ($xprofile && !empty($xprofile->username)) {
                $username = $xprofile->username;
            }
        }
    } catch (\Throwable $e) {
        // ignore
    }

    if (!$username) {
        $wpUser = wp_get_current_user();
        if (!empty($wpUser->user_login)) {
            $username = $wpUser->user_login;
        }
    }

    if (!$username) {
        return $items;
    }

    // --- Build absolute user URL and force https scheme ---
    $fullUserUrl = untrailingslashit($Helper::baseUrl('u/' . $username));
    $fullUserUrl = set_url_scheme($fullUserUrl, 'https'); // force https

    // Token map (support several formats, since UI sometimes strips braces)
    $tokenMap = [
        '{{user_url}}'  => $fullUserUrl,
        '{user_url}'    => $fullUserUrl,
        '#{{user_url}}' => $fullUserUrl,
        '#user_url'     => $fullUserUrl,
        'user_url'      => $fullUserUrl, // last-resort fallback
    ];

    /**
     * Normalize URLs to prevent:
     *  - http://https//example.com/...   (missing colon)
     *  - http://https://example.com/...  (double scheme)
     *  - http://http://example.com/...   (double scheme)
     *  - scheme-less malformed inputs
     * Always returns https://... when it looks like an absolute URL.
     */
    $normalize_url = function ($url) {

        if (!is_string($url) || $url === '') {
            return $url;
        }

        $url = trim($url);

        // Fix the specific broken form: http://https//example.com/...
        $url = preg_replace('#^https?://https//#i', 'https://', $url);

        // Fix double scheme: http://https://example.com/...
        $url = preg_replace('#^https?://https?://#i', 'https://', $url);

        // Fix double scheme: https://http://example.com/...
        $url = preg_replace('#^https?://https?://#i', 'https://', $url);

        // If it starts with http://, upgrade to https://
        if (stripos($url, 'http://') === 0) {
            $url = 'https://' . substr($url, 7);
        }

        // If it is a valid absolute URL now, force scheme again (belt + suspenders)
        if (preg_match('#^https?://#i', $url)) {
            $url = set_url_scheme($url, 'https');
        }

        return $url;
    };

    // Recursively replace tokens & normalize URLs
    $walk = function (&$node) use (&$walk, $tokenMap, $normalize_url) {
        if (!is_array($node)) {
            return;
        }

        // Common keys used across FCom versions and menu builders
        $urlKeys = ['permalink', 'url', 'link', 'href', 'permalink_url'];

        foreach ($urlKeys as $key) {
            if (!empty($node[$key]) && is_string($node[$key])) {

                // Replace tokens
                $node[$key] = str_replace(array_keys($tokenMap), array_values($tokenMap), $node[$key]);

                // Normalize final URL
                $node[$key] = $normalize_url($node[$key]);
            }
        }

        // Recurse children
        foreach (['children', 'items', 'sub_items'] as $childKey) {
            if (!empty($node[$childKey]) && is_array($node[$childKey])) {
                foreach ($node[$childKey] as &$child) {
                    $walk($child);
                }
            }
        }
    };

    foreach ($items as &$item) {
        $walk($item);
    }

    return $items;

}, 50, 2);