On this page of the Diablo 2 Resurrected guide, you will find the answer to whether you can use two weapons in two equipment slots at the same time.
The answer to the question is yes. However, only Barbarians are able to use two weapons. He even has dedicated skills to support the use of two weapons, and it's the greatest advantage of this hero. Other classes can use two equipment slots to wield two-handed weapons or bows (one slot is for a weapon, the other for ammunition).
Interestingly, a Barbarian can simultaneously use two weapons that are completely different from each other - not only by class but also by type. So he can wield an ax and a sword (of course, only the one-handed ones) - however, this is not recommended due to the special passive skills that improve only a particular type of weapon. There are many advantages of using two weapons when you have two with different bonuses. Barbarian can also use two knives/axes to throw and throw them at once (also has skills to improve it).