I did a stint in management, before I figured out it wasn't for me. In my country that involves getting into university level management courses, networking with other managers and getting a mentor. At least if you're working in an organisation that values its employees. Throughout it all the truest thing I ever learned was from my mentor who was one of the best managers I have ever worked with, and this is a direct quote. "Nobody is irreplaceable, sometimes it's expensive to say goodbye to someone, but nobody is irreplaceable.".
Over the decades this has proven itself to be true so many times. I've been part of big enterprise organisations as well as smaller startups that had some "vital" proces which relied on that one person. When they left however, it didn't really change anything in the big picture, sometimes it let to the entire guts of a company getting ripped out and replaced by something different, but in the big picture it just became another thing to solve.
I think it's a good thing to learn, both as a manager but also as an employee. Because at the big picture, what "irreplaceable" really means is "liability", and that's not a great thing to be at a company.
Good managers will work with you on how to reduce your importance, and great employees will know how to do so themselves. In the world of work, a good work relationship is one where the organisation you work for give you opportunity to grow, and sometimes that means, outgrow the organisation itself. But it goes both ways, and you should try to respect that, even if you're the rockstar employee because it'll make you even more valuable.