You seem to be right. Seems that now my previous link redirects to https://openai.com/news/rss.xml. I guess there is now an official feed again. Although it seems the posts in the feed are not in chronological order. Then again most RSS readers should handle that with no problem when sorting.
NOTE: I had trouble getting this feed to work on RSS Guard. When I asked the dev about it, he didn’t ran into any issues. For me, changing IP addresses, user-agents, RSS readers and even OS’s did not fix the issue. Making it weirder was that the feed was still accessible via a browser and curl with a correct user-agent parameter. Turns out RSS Guard has a feature to enable “HTTP/2.0” and when I enabled that feature, the feed magically worked. I don’t know if this is the correct solution, but I am documenting it anyways in case someone comes across a similar issue.