Looks like Lemmy "sub-reddit" are activitypub groups and thus can be followed: @technology
I never played around with it, but I can't imagine there being a way, without removing the original post.
Like, it's not technologically impossible, but your instance would need to issue the command for deletion, as you only have an account there. And then you'd need some UI to say that you want the post deleted specifically on the lemmy.ml-instance.
It starts to become rather complicated. 😅