Hi,

As I checked, here is your RSS feed URL:

https://ruttgaizer.com/index.php/feed/

And it doesn't update the content inside it to fit with your RSS you should have now. It still showing the "hello world!" posts.

It seems that related to a plugin you're using or your site config from the beginning. It's not an issue related to the theme because we don't have any code affect to RSS feed inside the theme. 

So, I can recommend you check 2 points below:

1/ Please try to deactivate all plugins ( except plugins come from the theme ) and try it again. After that, you need to wait for 12 hours to get RSS link updates the content. By default, RSS feed is cached (stored) for 12 hours on your server to improve website loading performance. Therefore, It should be refreshed every 12 hours automatically. When it has done, check it again, if RSS feed updated the content and works - that means you have a plugin caused this issue and you need to find what's the plugin caused that issue by check with each plugin.

2/ If point 1/ doesn't work - please try activate a default theme from WordPress ( twenty fifteen, twenty sixteen... etc ) and try it again. If it still doesn't work - that means you have something wrong config from the beginning - and you need to contact the hosting provider and ask them about this.

Best Regards,

PenciDesign