I think this works only if the user is from the same instance. If the user is from a different instance it opens up a new tab just like before.
I am really happy to see it working for the posts from same instance but would also like if like the mastodon FE it could also do it for posts from different instances.
I just checked and you are partially right it works for all federated Pleroma instances.
Sadly it doesn't work for all federated posts from Mastodon instances. I just checked after you mentioned it. Actually that might be also the reason why I was a bit late posting this.