I'm not sure exactly. It depends on which fictional universes or genres you're considering. Maybe in some popular fantasy worlds, there could be dozens or even hundreds.
Another wonderful fictional monster is the BFG (Big Friendly Giant) in Roald Dahl's book. Despite his huge size, he is a gentle giant who befriends a little girl. He is different from the other mean giants, and his character teaches children about kindness and not judging by appearances.
Often, they are physically imposing. For instance, a dragon in many stories is large, with the ability to fly and breathe fire, which makes it a formidable presence.
One of the well-known ones is King Kong. This giant ape-like monster has made quite an impression in cartoon adaptations. It's known for its strength and wild nature.
One reason could be that we want to appeal to a wider audience, including younger or more sensitive viewers. Also, making monsters less scary can focus more on their character development or the story's message.