If I could send one note back to the version of me starting out in this work, it wouldn't be about technology. It'd be about how little of the job is technology.
The younger version believed the answer was always more knowledge. Learn the next product, master the next architecture, be the most technically correct person in the room, and the rest would follow. So he optimised for being right, and treated everything else as noise around the real work.
It took longer than it should have to see that being right is the entry fee, not the win. The room doesn't reward the most correct answer. It rewards the person who understood what was actually being asked, who read what the customer couldn't say out loud, who could take something complicated and hand it back simple enough to act on. None of that is on a certification path.
I'd tell him to spend less time proving he knew things and more time listening for what the other person was really worried about. I'd tell him that "I don't know, let me find out" costs nothing and buys a surprising amount of trust. And I'd tell him the technical depth still matters, just not in the way he thinks, because its main job is to let you stay calm while you do the harder human part.
He wouldn't have listened, of course. Some things only land once you've got them wrong yourself a few times.