A function from the RSS plugin is not available in WebC template

I am working on a site that is using the eleventy-base-blog. I've been working on going full WebC templates and I ran into an issue while I was trying to convert the feed.njk

link to the original version of the file: https://github.com/11ty/eleventy-base-blog/blob/main/content/feed/feed.njk

here's my conversion of it to .webc

---
# Metadata comes from _data/metadata.js
permalink: /feed/feed.xml
---
<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom" :xml:base="metadata.language">
    <title @text="metadata.title"></title>
    <subtitle @text="metadata.description"></subtitle>
    <link :href="htmlBaseUrl(permalink, metadata.url)" rel="self" />
    <link :href="addPathPrefixToFullUrl(metadata.url)" />
    <updated
        @html="dateToRfc3339(getNewestCollectionItemDate(collections.post))"
    ></updated>
    <id @html="metadata.url"></id>
    <author>
        <name @text="metadata.author.name"></name>
        <email @text="metadata.author.email"></email>
    </author>
    <entry webc:for="post of collections.posts.reverse()">
                <title @html="post.data.title"></title>
        <link :href="htmlBaseUrl(post.url, metadata.url)" />
        <updated @html="dateToRfc3339(post.date)"></updated>
        <id @html="htmlBaseUrl(post.url, metadata.url)"></id>
        <content
            type="html"
            @html="transformWithHtmlBase(post.templateContent, absolutePostUrl, post.url)"
        ></content>
    </entry>
</feed>

This is the error I get from the above code:

[11ty] Problem writing Eleventy templates: (more in DEBUG output)
[11ty] 1. Having trouble rendering webc template ./content/feed/feed.webc (via TemplateContentRenderError)
[11ty] 2. Check the dynamic attribute: `@html="dateToRfc3339(getNewestCollectionItemDate(collections.post))"`.
[11ty] Original error message: getNewestCollectionItemDate is not a function (via Error)
[11ty]
[11ty] Original error stack trace: Error: Check the dynamic attribute: `@html="dateToRfc3339(getNewestCollectionItemDate(collections.post))"`.
[11ty] Original error message: getNewestCollectionItemDate is not a function

getNewestCollectionItemDate comes from the RSS plugin: https://github.com/11ty/eleventy-plugin-rss

here's my Eleventy config, it's the same one as the Base Blog with the addition of WebC and an extra filter

const { DateTime } = require("luxon");
const markdownItAnchor = require("markdown-it-anchor");

const pluginRss = require("@11ty/eleventy-plugin-rss");
const pluginSyntaxHighlight = require("@11ty/eleventy-plugin-syntaxhighlight");
const pluginBundle = require("@11ty/eleventy-plugin-bundle");
const pluginNavigation = require("@11ty/eleventy-navigation");
const { EleventyHtmlBasePlugin, EleventyRenderPlugin } = require("@11ty/eleventy");
const pluginWebc = require("@11ty/eleventy-plugin-webc");

const pluginDrafts = require("./eleventy.config.drafts.js");
const pluginImages = require("./eleventy.config.images.js");

module.exports = function(eleventyConfig) {
    // Copy the contents of the `public` folder to the output folder
    // For example, `./public/css/` ends up in `_site/css/`
    eleventyConfig.addPassthroughCopy({
        "./public/": "/",
        "./node_modules/prismjs/themes/prism-okaidia.css": "/css/prism-okaidia.css"
    });

    // Run Eleventy when these files change:
    // https://www.11ty.dev/docs/watch-serve/#add-your-own-watch-targets

    // Watch content images for the image pipeline.
    eleventyConfig.addWatchTarget("content/**/*.{svg,webp,png,jpeg}");

    // App plugins
    eleventyConfig.addPlugin(pluginDrafts);
    eleventyConfig.addPlugin(pluginImages);

    // Official plugins
    eleventyConfig.addPlugin(pluginRss);
    eleventyConfig.addPlugin(pluginSyntaxHighlight, {
        preAttributes: { tabindex: 0 }
    });
    eleventyConfig.addPlugin(pluginNavigation);
    eleventyConfig.addPlugin(EleventyHtmlBasePlugin);
    eleventyConfig.addPlugin(pluginBundle);
    eleventyConfig.addPlugin(EleventyRenderPlugin);
    eleventyConfig.addPlugin(pluginWebc, {
        components: "./_components/**/*.webc",
    });

    // Filters
    eleventyConfig.addFilter("readableDate", (dateObj, format, zone) => {
        // Formatting tokens for Luxon: https://moment.github.io/luxon/#/formatting?id=table-of-tokens
        return DateTime.fromJSDate(dateObj, { zone: zone || "utc" }).toFormat(format || "dd LLLL yyyy");
    });

    eleventyConfig.addFilter('htmlDateString', (dateObj) => {
        // dateObj input: https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#valid-date-string
        return DateTime.fromJSDate(dateObj, {zone: 'utc'}).toFormat('yyyy-LL-dd');
    });

    eleventyConfig.addFilter("year", () => {
        return DateTime.now().toFormat('yyyy');
    })

    // Get the first `n` elements of a collection.
    eleventyConfig.addFilter("head", (array, n) => {
        if(!Array.isArray(array) || array.length === 0) {
            return [];
        }
        if( n < 0 ) {
            return array.slice(n);
        }

        return array.slice(0, n);
    });

    // Return the smallest number argument
    eleventyConfig.addFilter("min", (...numbers) => {
        return Math.min.apply(null, numbers);
    });

    // Return all the tags used in a collection
    eleventyConfig.addFilter("getAllTags", collection => {
        let tagSet = new Set();
        for(let item of collection) {
            (item.data.tags || []).forEach(tag => tagSet.add(tag));
        }
        return Array.from(tagSet);
    });

    eleventyConfig.addFilter("filterTagList", function filterTagList(tags) {
        return (tags || []).filter(tag => ["all", "nav", "post", "posts"].indexOf(tag) === -1);
    });

    // Customize Markdown library settings:
    eleventyConfig.amendLibrary("md", mdLib => {
        mdLib.use(markdownItAnchor, {
            permalink: markdownItAnchor.permalink.ariaHidden({
                placement: "after",
                class: "header-anchor",
                symbol: "#",
                ariaHidden: false,
            }),
            level: [1,2,3,4],
            slugify: eleventyConfig.getFilter("slugify")
        });
    });

    // Features to make your build faster (when you need them)

    // If your passthrough copy gets heavy and cumbersome, add this line
    // to emulate the file copy on the dev server. Learn more:
    // https://www.11ty.dev/docs/copy/#emulate-passthrough-copy-during-serve

    // eleventyConfig.setServerPassthroughCopyBehavior("passthrough");

    return {
        // Control which files Eleventy will process
        // e.g.: *.md, *.njk, *.html, *.liquid
        templateFormats: [
            "md",
            "njk",
            "html",
            "liquid",
        ],

        // Pre-process *.md files with: (default: `liquid`)
        markdownTemplateEngine: "njk",

        // Pre-process *.html files with: (default: `liquid`)
        htmlTemplateEngine: "njk",

        // These are all optional:
        dir: {
            input: "content",          // default: "."
            includes: "../_includes",  // default: "_includes"
            data: "../_data",          // default: "_data"

            // during development we build to, and serve from, the gitignored _site folder
            // during production we build to the docs folder, which is served by GitHub Pages
            output: process.env.ELEVENTY_RUN_MODE === "serve" ? "_site" : "docs"
        },

        // -----------------------------------------------------------------
        // Optional items:
        // -----------------------------------------------------------------

        // If your site deploys to a subdirectory, change `pathPrefix`.
        // Read more: https://www.11ty.dev/docs/config/#deploy-to-a-subdirectory-with-a-path-prefix

        // When paired with the HTML <base> plugin https://www.11ty.dev/docs/plugins/html-base/
        // it will transform any absolute URLs in your HTML to include this
        // folder name and does **not** affect where things go in the output folder.
        pathPrefix: "/",
    };
};

11ty / eleventy-plugin-webc

A function from the RSS plugin is not available in WebC template #90