Here is one thing to watch out for before reading Conspiracy Research Club-
The art style (and plot). With the art style, it usually seems cute and happy, but at the same time some pictures in it are enough to give ME nightmares, considering when I close my eyes is see pictures from CRC now, and I don't scare easily and have watched and read a lot of scary stuff in the middle of the night before. Though if you do read it and find these images, one tactic I use to keep myself from being scared it to turn a scary image into a funny, cute or happy one. Maybe turning a killer clown into a drag queen, a room full of dolls into puppies and kittens, corpse-y looking people into ridiculous hippie clothes (including sunglasses if like me the eye sockets freak you out). Whatever makes you laugh or happy, try changing the image in your mind a bit. The main part of CRC that scares me is corpse-y looking people and the glitchy static stuff. I replace the corpse people with hippies and drag queens and the glitching screens with scenes of My Little Pony and such. And try not to directly look at what scares you too much or it will get stuck in your head and you will see it when you close your eyes.
GemHeart Sounds like my sort of manga. BUT I'LL HEED YOUR WORDS, I'M NOT TOUCHING IT
KnightStar that used to happen to me when I was younger, but now literally nothing scares me. I used that A LOT. I even thought of animal fairy creature angels blessing me to sleep, and they were my go-to thing. Anyways, I guess the only thing that scares me are what I see irl.
Queeny Bruh I read junji ito's "Enigma of Amigara Fault" at like 2 am at night by myself. I am desensitized to most horror lol