What did you add to your site to make the posts show up in forward chronological order, rather than the more normal reverse chronological order? Seems that whatever is doing that is incorrectly affecting your feed as well.
A blog is a series of posts in reverse order by time. Latest post first, basically. But your site appears to show them the other way around, from oldest first.
A feed isn’t “updated”, it’s just another view of your site. Instead of showing each post on a webpage, it shows each post in an RSS feed. That feed also needs to be in reverse chronological order, so that new posts push old ones down. Because the feed isn’t meant to show all the posts, only the most recent 10 posts or whatever you have it set to show.
So, whatever you have making it show the posts oldest first needs to be changed to not do that for the feeds.