[panny]

You're working where they want cogs, interchangable cogs. They don't want you to build something special and be the only one who knows how it works. You could leave, and then they are screwed trying to support the thing you wrote. It sounds like you've already done some of this by your own description. You're not a senior, and you're busy trying to prove you are senior material, right? But if you really want to be senior, you need to do dull things that you are skipping. Documenting, collaborating, keeping everyone in the loop, sharing all the information you have as best you can.

Want to really be a senior? Think this way: Everything I build as a senior developer is an attempt to make myself obsolete. I should be able to give a two weeks notice and walk away with no harm to the company. When I build things at work, I never worry about job security, not even a little. If there is something I built that they can't support without me, I've failed.

And you will ultimately know you failed when you can't even go on vacation without carrying the company laptop with you. I know you're proud of that thing you built and how you're the only one who knows how it all works, but that's the core problem.