How do I get my blogdown blog on R-Bloggers?

In the Hugo documentation (https://gohugo.io/templates/rss/), they provide the embedded RSS xml file that currently "ships with" Hugo. According to the docs, a section’s RSS will be rendered at /SECTION/index.xml (e.g., http://spf13.com/project/index.xml). So for your posts, it would be http://spf13.com/post/index.xml.

The key line in the built-in RSS xml file is this one:

<description>{{ .Summary | html }}</description>

From this discussion (https://discourse.gohugo.io/t/full-text-rss-feed/8368/2), it looks like you want to change what goes in the description tags from .Summary to .Content. Here is an example blog post where the author implemented this change: https://randomgeekery.org/2017/09/15/full-content-hugo-feeds/

So you would change that one line in the Hugo RSS xml to:

<description>{{ .Content | html }}</description>

The full rss.xml file should live in your layouts/ folder, with that one line changed.

It does look like there are other options you could test, like working with output formats in your config.toml file (https://github.com/gcushen/hugo-academic/issues/346; https://gohugo.io/templates/output-formats/) and referencing your RSS in your header.html (https://gohugo.io/templates/rss/), but changing .Summary to .Content should address your issue.