You can try the notation [html](file:///path/to/file.html).
This is not a replacement for internal links, since this notation does not allow relative paths. So as soon as you move your vault elsewhere, these links will all break.
We never supported this.
I considered it a bug, since the behavior is not consistent, even if it never worked. But you’re right, strictly speaking it’s not a bug, so raised this as a feature request now.