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

Why doesn't the Altar of Transformation (WoG object) work in ERA 2.461? Is this happening to everyone? And how can I fix it?

What does the HD mod branch have to do with it? That's the first thing.
Secondly, the Altar works. I just checked it right now. Maybe you just needed to enable the script in the WoG settings?