I experienced some trauma several years ago online. Basically I had suicidal depression and some other issues. I went online and people were (unprovoked) telling me that my current condition warranted suicide, they gave reasons that sounded solid and well-rounded, they told me how I could do it so it wouldn't hurt, etc etc etc. I started trying to kill myself until I was forcibly barred from using the internet. I don't really feel like killing myself anymore but to this day I still have a lingering phobia of the web and I can't use it without supervision and limits. And a lot of the reason it that I'm afraid of people online. Without meaning to, I find them saying really upsetting things, and I can't get over it.
I know some spells for keeping people away from me, but they're intended to target specific people I've met in real life. Are there spells to keep venom-spitting strangers away from me while I'm online? I see really disturbing photos online, too, pictures of bad injuries and pictures with upsetting captions, and I'd like to keep those away. I'm currently using pictures of animal "guardians" on my desktop, but I don't think it's enough.
Also... I don't know if I'll ever do it, but... is it possible for me to cast a curse on somebody I've only seen online? Sometimes I get really angry about how there don't seem to be any consequences for anyone's words or actions now that the internet exists, and people like me have died because of it. There's the Rule of Threes and everything but... every time I see someone urging a 10 year old girl to kill herself or cheering for a mass-shooting, I feel like I want to make them pay...
Sorry to hear you went through that. Experiences like that are difficult enough, and having people act like that about it is awful.
You could use controls that parents use to filter upsetting images from their kids. Some sites also allow people to input hashtags and words they don't want to see. It doesn't entirely prevent things from getting through, but it can help.
I have some similar issues with upsetting images and content online, and if I'm having a particularly bad day, I'll usually only use sites with strict and well-enforced rules on what can and can't be posted, or I'll only go on articles and videos I've read or watched before. It isn't ideal, but it can be helpful on a bad day.
As far as magickal solutions, if you've found a banishing spell for real life situations, you can rewrite it to target people online. You could also keep things around your computer that banish and purify: light a black candle for a few minutes before getting online, keep purifying crystals around your computer, set salt on it when you aren't using it, etc. You could also put things in your online profiles that are banishing: a profile picture with colors associated with banishing, a small incantation in your bio, a sigil in your pictures.
I personally believe it's possible to curse people online. It would be easier with information such as the person's name and if they had pictures of themself, but in my opinion it's possible if you pull their profile up. I don't believe in the Threefold Law, though, so I can't give much input on that.
Even with the use of magick, it's possible that you'll still come across unwanted content online, so if you haven't already, you may want to seek counseling or therapy to help you overcome the fear.