chris_swe

The plugin WP External Links is interfearing with the plugin, open the settings screen for WP External Links and add “googleusercontent.com” to the ignore URL’s containing….

Or use https://www.canis-dirus.de/public/wordpress/feed (without trailing backslash) . Your feed works on my Flipboard account.

Should work out of the box with the plugin enabled, what is your feed URL?

I can recommend PhotoSwipe – open source and works very well without much work.
https://www.photoswipe.com/