LGBTQ+

I think the best protocol is report the bad actor, not engaging with them (especially inserting yourself into a situation you're not already in), working on personal tolerance for verbal abuse and tactics for healthily managing feelings that come with getting bullied, and ultimately knowing when to remove yourself from a situation when it's not beneficial for you any longer.

Remember that online harassment that you speak of generally falls under trolling. Trolls do things "For the lulz". Their goal is to entertain themselves by getting other people mad, sad, upset, or making a scene. If you don't take the bait, you can minimize the benefit they get out of trolling.

Getting familiar with privacy/safety settings on site you frequent is important for addressing targeted harassment.

To address your question, I don't know if showing a victim that someone cares is necessarily what ALL victims might want, you are just some random anonymous user to them. They may just want to not talk to people, or to talk to people they trust. Recognizing boundaries is important, especially when someone has been the victim of someone trashing those boundaries through harassment.