So, we managed to have RSS-stream onto a federated website, including images! Many improvements are in our checklist, but for now let's recap the requirements for any website wanting to join
We baptised this system RSF - Really Simple Federation
This step is necessary in order to be able to communicate in a secure manner among federated websites
WP is the technology running under the hood of ~40% of total world websites, thus is important to have a clear procedure to make this kind of website easily RSF-compatible!
Two steps are required. One optional step can be performed to widen the choice of content exposed with RSS feeds.
upgrade&update your WP instance
install the add image to feed plugin by Lesion.
There are a lot of plugins in the WP ecosystem to match this necessity, that is, to expose images and featured image to RSS. But often they have other requirements-dependencies, sometimes they are discontinued, they present many configuration options, and they are all more complicated than this one counting only 45 lines of clean PHP code, coded exactly for this purpose, and approved by WP.org.
a few possibilities:
3.1. Create RSS feed separated for category - NO coding
3.2. Create RSS feed separated for category - customised, coding capacity needed
3.3. DIY for create, customise WP RSS - customised, coding capacity needed
install&enable the grav plugin feeds and configure it as you prefer, here the docs.mazizone.net one