HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

There are still many things that don't work in WT... and it seems to me that nothing has been done except for 8 heroes in the list, an extended screen, displaying mana, and fixing bugs. And HD+ is only for SoD, right?

Well, that's pretty much the case. For example, the quick transfer buttons in HD style don't work. This is probably due to the presence of scripts. However, I personally don't see any objective reasons why the highlighting shouldn't work. Maybe I just don't know all the nuances.