Try to notice why I find it so upsetting, and see if I can unpack and defuse it.

I start by not getting bothered by stupid shit said by people I don’t know and don’t care about. Only people that I know and respect have the capacity to hurt me in any way.

My response comes down to what I feel the other person's intent is. If they're a troll, I don't engage to begin with - downvote and move on. If we entered into a conversation but I find that they're arguing in bad faith (they want to argue, not reach an understanding), then I say something like "I'm not going to argue with you about it, but I appreciate your perspective" (even if I don't). If it seems like it could be a useful disagreement, though, I'll consciously remind myself that there's a person behind the text, and I'll continue the conversation until it reaches an end. It may be uncomfortable, but remembering that we're all just humans being human helps me tone myself down.

The first step for me was realizing that this stuff made me angry and unhappy. Rather than viewing this as something I need to exercise my anger on I view it as something I need to avoid so I don't get angry. Using the block feature really helped a lot.

Turn your notification off and do something else. It could be anything, the better version would be go outside and talk to other people.

However, just watching Youtube video from someone you like, still works. At the end of the day, online argument is not a real argument.

As soon as someone starts engaging with me in a rude way online, I respond with one single "hey let's chill out" or "we can disagree peacefully" kind of comment. That gives them a chance to stop being confrontational.
If they burn that chance I either disengage or troll you into the abyss (depends by how much free time I have in that moment) because I know that arguing with angry people is useless.

Do you regert having involved in an argument itself or what

'Murica bad people

either ignore it or use factual calm statements to lure out personal attacks and then report them. I got a bunch of people banned from reddit this way before I was banned for "threatening violence" in a comment where I didn't threaten anyone at all, or mention any violent acts. Things are much calmer and more "adulty" here. Besides any political discussion of course.

Be thankful that this is the biggest problem I'm facing!