Really it depends. Most the big names kinda aren't as they move in ways unknown to us and we are lower than dust or bacteria to them. Or even a part of them. Ubbo-Sathla, Daoloth, Atlach-Nacha, etc etc.
However the more...., actual interaction a 'deity' has with humanity the more malevolent we can call them. We can get away with calling Cthulhu malevolent due to his followers acting on earth. Nyarlathotep too but he does it more out of boredom and needing to share his suffering with others though he's also a plans within plans kinda of deity so might help to hurt later down the line if it's a bigger impact.
Then you kinda get into the less well known guys like Yig, Ithaqua, Glaaki and Chaugnar Faugn. Who are malevolent but tend to be in the smaller scheme of things(Mind you these are still beings of inhuman power so, scale is messed up)
Mind you there are some debates about if they are Elder/Outer gods or just strong beings. But they are beings that are currently on or are acting on earth even if it's through cultists.
However the more...., actual interaction a 'deity' has with humanity the more malevolent we can call them. We can get away with calling Cthulhu malevolent due to his followers acting on earth. Nyarlathotep too but he does it more out of boredom and needing to share his suffering with others though he's also a plans within plans kinda of deity so might help to hurt later down the line if it's a bigger impact.
Then you kinda get into the less well known guys like Yig, Ithaqua, Glaaki and Chaugnar Faugn. Who are malevolent but tend to be in the smaller scheme of things(Mind you these are still beings of inhuman power so, scale is messed up)
Yig is probably one of the more even and yet unknown guys. "Father of serpents" he's easy to anger and please. Just don't mess with him really or snakes and snake headed cultists are gonna show up. He tends to get fleshed out in other material such as Pathfinder or games. What his goals are who can say but he's one that takes an actual hand in doing stuff on Earth
Ithaqua is basically Wendigo. On steroids. He's got a cult acting on earth and those that live in the frozen places of our planet tend to live out offerings in order to bribe him off. Ithaqua also has a bunch of monsters/servants and tends to kidnap(read drag) people to an ice world he rules. Some to kill and maybe eat. Others to press into worshiping him there. Also has a thing for trying to mate with women to produce a being that can surpass himself and free the rest of the old gods. Not good news for us but more personal and tends to be understood. Comes in kills and freezes and then drags people back to horrible fates.
You live in England? Well you got Glaaki, a giant slug like being with metal spikes living in a large lake. Knowledge and magic are his stick though the knowledge is mainly about other things living nearby or associated with water. Many call upon Glaaki for either knowledge or immortal life. Unsure about the first one but the second one he gives out freely; driving a metal spine into them and giving them an injection. Problem is this turns them into zombie like servitors that can't stand the sun as they 'age' into this new state. What he does with the cultists is anyone's guess.
Chaugnar Faugn 'the Elephant' is this, thing that combines the worst aspects of octopus, elephant, and human being. He's got his own cult; the Tcho-Tcho people. At first he was worshipped by amphibians when he first arrived on earth but he made those things into servants and then had those mate with humans. Said hybrids would become the Tcho-Tcho years later, who are kinda cannibalistic. Chaugnar himself uses his trunk to drink blood from beings that are brought to him. Now he doesn't seem to be an outright threat but some expanded materials seem to point towards his people trying to spread worship of him..., and thus the practice of cannibalism. Ugh...
Mind you there are some debates about if they are Elder/Outer gods or just strong beings. But they are beings that are currently on or are acting on earth even if it's through cultists.