Without notice and any further ado, Ubisoft shut down online servers for around 90 older games, to date 27.4.2022. There check full list.
The list is long and includes Heroes of Might & Magic V, as well as Might & Magic: Clash of Heroes.
All online bonuses will remain permanently off:
For games that used Ubisoft Connect services, Units and Challenges will be disabled, meaning you will no longer be able to earn Units by completing Challenges for the game.
Unlockable content (ULC) such as maps and skins will also be disabled, meaning that you will no longer be able to unlock them.
On PC, ULC will no longer be available even if it has been redeemed previously. On console, the ULC will continue to be available unless you reset your saved game files.
Oh, geez, guess I shouldn't be surprised. After all, even if they ressurected M&M: Legacy X as offline, you need to buy it over Steam as Ubisoft e-shop has a black hole instead it.