Document any relevant interaction with that colleague. Talk to your boss about the situation, state the facts, how they affect you and your work. When talking to your boss, put the focus on what you can do in order to have a professional work relation with your colleague rather than sounding accusative.
People don't change. Not really, anyway.
They can be open minded about self improvement, and learn to manage any negative personality aspects, but they don't fundamentally change.
Petty, solipsistic (self-centered, thinks the world revolves around him. Almost narcissistic - ex: you finding a mistake in his code is not simply a correction, it's a personal ...
Write this down
PEOPLE DO NOT CHANGE
if he was and is a vengeful dush that cant accept criticism, he will remain that.
Maybe, like 0.00001% after your talk he will hide and try to look different,
remaining the same inside and waiting for his opportunity to destroy you.
Do you want to take this chance?
What can I do to identify the root problem and how can I solve it in general?
Instead of trying to solve the root cause, just ask him directly what he wants and what would it take for him to enjoy his job and stay here. If it is just an issue of using (or not using) Slack or some other tool, it should be reasonably within your power to allow him that ...
my management style so I'm trying to figure out what I need to change.
Yes, you're getting too involved on a personal level.
You should give praise where it's due, reassurance likewise, but not get involved in much dialogue over either. Managers should take a step back from people's personal issues and let them handle those themselves. You're a manager, ...
Is the real problem actually with this developer at all?
You say he's your best - producing quality code, technically highly literate - but he feels he's a bad fit for the team, based around rather more nebulous ideas of velocity and responsiveness. Are the rest of the team making rapid progress (or at least, the illusion thereof) by doing shoddy work? Are ...
today he said that he actually gets more work done when he closes slack and tunes out from all the messages
Well, you have your answer. He cannot do all he can do, because of the interruptions. This is not a mild thing, it is very important.
To understand it better, read more about the flow state of mind.
To be bale to handle the situation better, try to ...