Do you think that Stanley suppresses his hard-won intellect once Ford comes back and they get their happily ever after?
Like, Stan understands that he had to learn and do this hard work in order to restart the portal, but he's got such bad imposter syndrome that he can't conceptualize what an accomplishment he achieved. Ford was too arrogant and angry at the time to recognize it, the kids are too young to fully comprehend it, pre-recovery Fiddleford would be too confused to really remember the effort it took to make it, and everyone else would simply be so out of the loop to even understand what happened. Stan can only see what he did through the lenses of "fixing my mistake". I wouldn't put it past Stan to think that he's still not smart because he "basically followed Ford's instructions" without adding in the context that a lot of the instructions were gone or nonexistent or that the physicality of the project was dangerous and volatile or that he was basically having the start from the bottom up in order to even understand Ford's "instructions". Stan thinks that the effort put into opening the portal was him, once again, "riding on his brothers coat tails."
But that doesn't stop Stan from now understanding. Things that were once complete and utter nonsense and gibberish, now make logical sense, to the point where he can even make his own sound and scientific conclusions.
Because all that time was focused on opening the portal and only the portal. So to see it pop up as a skill, where he may actually be able to provide genuine input to a complex problem really messes with him. He's not the smart twin. That's not his role to play. He's not always the bad twin, but he knows that he'll always be the stupid twin.
So when Ford and Stan go sailing, Stan pushes down those skills. He may have a few complex's about losing his role as the "Brawn" between him and Ford, as he is aware that Ford had to become a fighter in order the survive (which Stan does not complain about. He's glad Ford can stick up for himself now, it's all he ever wanted. But that doesn't stop himself from feeling his heart break at the idea of not being needed.) But he knows that he has his happy ending and he doesn't want the ruin it.
He feels himself sometimes wanting to contribute to a conversation with Ford about one of his machines or about an experiment or hell, sometimes, even the portal, which Ford has never asked him about. But he fears that he's going to open his mouth and Ford is going to give him that look of pity, that "That was a good try" smile, a "Well, actually" speech. And he doesn't know if he could handle opening up about maybe, possibly, in a blue moon, being smart too only to proven again that he was never smart and he should leave that to the professionals.
I do have this idea of Stanley sneakily going behind Ford and going over his experiments and machines when they are giving Ford trouble to see if he could possibly figure it out. Not because he thinks he's smart, but because he hates seeing Ford so upset. And when he realizes a mistake or where Ford is hung up on, he'll fix it for him and then wait to see what happens afterwards. He only does it when he knows Ford is being particularly upset about something and has been worked up about it to the point where he's getting frustrated and awake for days on end. Usually this means that he's not as perceptive to changes. Stan will finally make Stanford take a break, eat something, take a shower, do some love making, go to bed, anything to make him calm down and away. And when Stanford is preoccupied, he'll take a look.
And it works. Ford doesn't realize his work has been tempered with and instead just thinks he got too into his head. Stan tells him that this is why he should take more breaks and listen to him when he says it's time for breakfast/lunch/dinner or bed. Ford always feels sheepish afterwards, believing that Stan is right and he should take more breaks. Stan feels accomplished when this happens, that he did something that Ford couldn't provide for himself. He was needed and wanted while still letting Ford remain the smart twin.
But it doesn't last forever. Stan puts Ford to bed after he was messing with a piece of machine for over a week, frustrated and cranky because it refused to work. Stan goes to review the machine, going over his equations and looking over the components. Slowly, he starts tinkering with the machine, fixing the equations and bringing the machine to life. What Stan doesn't know is that Ford woke up with renew vigor earlier than Stan thought he would and went down to his lab to work on it, only to stop dead in his tracks. Watching in the shadows as Stan works on the machine until it finally works. But, something strange happens. Right after Stan gets it to work, he "breaks" it in a way where it would take only a few moments to refix it. He fixes the work shop as it was when Ford left it.
Then it dawns on him. Stan was working on the machine just enough for Ford to come back and finish it, believing that he fixed it.
While Ford is so transfixed on what he just saw, he doesn't realize that Stan has caught Ford staring. And when Ford realizes he's been caught, he doesn't move. He stares at Stan and really looks at him. Wonders how long had he been doing this, what else has he been able to do, why is he hiding it, how long has he been able to help out? Why didn't he tell him. He didn't ask though because he already knew the answer. Ford takes Stan by the hand and brings him back to the work bench and sits them both down. He moves the machine back over to him while he looks over his equations. He's asking Stan to fix it for him, but Stan is scared. This isn't his role, but Ford is asking him to do this, Ford is trusting him to do this. So he does.
And Ford takes Stan's hand.
And Ford looks at Stan like it's the first time they've met and realizes that he has yet to know everything about him and falls in love all over again.