All questions regarding mapmaking for Heroes of Might and Magic 3: The Shadow of Death.

I wanted to give the hero a club,
but in the game, it turned out that he has two clubs:
one in his hand, and the other in his backpack (SoD)
how to fix it?

I've never had any problems with giving out artifacts... It seems that two artifacts were accidentally specified: one in the hand, and the other in the backpack.
If everything is normal there, then upload the map - let's take a look.

another question: there is a "rumors" tab in the specifications.
how do they manifest during the game?

When you enter the tavern, you can read a "rumor" above the heroes. Every week, a new "rumor" is displayed, which is chosen randomly from those set by the game developers and those created by the map author (in the map specifications, the "Rumors" tab).
Rumors do not have any other function besides being informative.