There are some weapons which can be equipped but then can't be used in battle. No fight option in the menu.
Happens with poignard, hammer or rapier for rangers, wand or bullwhip for mages. They are compatible with the character profession and correctly report attack and damage statistics.
I can't understand what's going on. Is this a bug of this GOG version ?
See screenshots.

The weapon whose stats you've shown has a "(S)" after its name. This means that this is a short range weapon. Short range weapons can only be used to attack from the front row (first three slots).

Your mage is in the fifth party slot, putting in her in the back row. This means she can't attack with short range weapons from that position.

If you want to attack the enemy physically, you need to do one of the following:
* Put the character in one of the first three slots (not recommended for a mage; it makes the character vulnerable to enemy short range physicals)
* Equip a longer ranged weapon (one with (M) or (L) by its name), and attack with that
* Have the character hide, than attack from the shadows. (Requires Ninjutsu, which only certain classes get (Ranger being one of them). However, if you have at least 1 point in his skill, the skill, and then change class, you keep both the skill and the ability to hide, and (unlike in 8) can continue to improve it.)

Yeah, make sense. I don't know, I was sure I used short weapons from the back. Probably not.
Anyway bullwhip is extended and actually works.
Thank you.