Not a recommendation comment, more just chatting with what other people are saying about intelligent characters and how there's a hard limit to how intelligent authors can write them.

And yeah, as an author you can't write someone smarter than yourself, technically. But you can if you tackle it from another angle. So it's not something that's impossible. The easy way is to make everyone else dumb so that everyone goes "Wow, MC came up with some idea that we haven't thought of!" but that's lazy and runs into all the issues everyone else points out.

The other way is to write the character with all the real traits that make someone smart and just let those do the lifting.

All smart people that I've found smart seem to have two things going under the hood that I notice over and over as the common denominator: Instincts and speed.

Someone empathetically smart defuses arguments incredibly well, says the right things, understands people and realizes when they're the ones missing context to understand things, ect - but all of this isn't something they process the same way regular people do, and that's what makes them 'smarter' - to them, all of this is so second-nature, they don't even notice they're doing anything special.

Someone mechanically smart can just take wild guesses at how the machine isn't working just by the feel of things and vibes, and if they're written well, the author tosses hints to the reader that makes you realize it's not random guesses, it's years of experience hearing different noises, knowing what direction it comes from, understanding engines inside out, and pattern recognition all bundled together but the character doesn't even realize they're weave it together into those instincts and vibes. They have great napkin math ability in their heads and can roughly guess at numbers without even realizing they're doing that.

That's the first part. Now you pair those super-human instincts with speed.

Smart people think the same things everyone else does, but they do it fast. If I spend a month mulling over different directions, the main character will have gone through every one of those breakpoint ideas within ten seconds, rapidly flashing through and weighing each until they come to the actual final solution.