Probably one of the most famous examples, but the robots in The Matrix originally kept humans around as wetware CPUs using their spare brainpower. Studio execs forced the Wachowskis to change it to them using humans as batteries, even though that makes no sense. Agent Smith possessing someone in the real world in the sequels would have made a ton more sense with the original explanation.

A little bit more emphasis during Star Wars that Vader wanted the Storm Troopers to aim poorly and let them get away. It would have solved decades of jokes and arguments about Storm Trooper weapon accuracy.

“So, we started using teleportation now.”

• Everyone in Game of Thrones from season 6 onward.

I kinda think that if you can imagine a one-line fix to a plot hole, it isn't really a plot hole.

I remember someone insisting to me that there was this huge plot hole in the film of the Fellowship of the Ring, because Merry and Pippin don't get told about what Frodo and Sam are actually doing until the Council of Elrond, but still willingly run around risking life and limb to help them. Now, not only is this not a plot hole in itself (I'm pretty sure I'd help anyone fleeing a demonic horseman, just on principle, never mind if that person was my lifelong friend/cousin), it's also quite obvious that they could have been told everything offscreen. The audience didn't need to hear all that explanation again, five minutes after we first heard it.

A lot of plot holes people like to complain about are basically of this nature. 'Can you imagine a fix?' Yep, easily. 'Did the audience need to hear it?' Nope, because I could easily imagine it. 'Well, there you go, then.'

I'm digging deep in my memory here so I can't provide any details, but there was one episode from a very early season of Grey's Anatomy where I got to the end of the episode and thought, "wait, did they ever solve this episode's medical mystery?" There was a lot of doctor-plot that episode and the patient plot just kinda got dropped. Well I watched the deleted scenes for that episode, and low and behold there's a line where they explain exactly what was going on with the patient. It wasn't the real highlight/purpose of the scene, but I'm still shocked they would cut it because it left an entire plotline (albeit just for that episode) completely dangling.

The Kessel Run being measured in distance rather than time could have been solved with a closeup shot instead of wide angle.

The way it's scripted, Han thinks he's got two local yokels and is feeding them a line. Obi-Wan, of course, is not a yokel, and reacts to that info with a "come on, dude" kind of look. Alec Guinness does do it, but not in a noticeable way. If there was a closeup shot, it would have worked. The wider shot that went into the film makes his reaction barely noticeable.

This leads to decades of treating Han's line as actual truth and trying to figure out what he meant. Legends and Disney canon provided basically the same answer. Kessel is surrounded by black holes, and skimming closer to the event horizon would mean taking a shorter distance. Wasn't supposed to work that way, though.

The Martian when the main airlock blows up.

He ends up taping a plastic sheet over the hole with what I assume is super strong space tape and plastic and then continues to live in the station for 550 more days.

We spend the first half of the movie learning how unforgiving the environment is, and how delicate his ecosystem for life is, but you can also blow half the place up and just tape some plastic over the hole.

They did a much better job of explaining it in the book, but the movie literally went "just tape that bitch up with plastic, then we'll throw a wind storm at it to prove it's good forever"

“Eagles can’t fly us to Mt. Doom because of a magic curse or some shit”- Gandalf to the council in Lord of the Rings

Kinda the inverse of your question (or an example of this being done poorly) but in the latest or (second to latest) star wars, after being accused of recycling the old trilogy plot over again, the writers attempted to deflect away from the obvious similarities to Hoth by having one of the characters taste what appeared to be snow on a frigid planet resembling Hoth by exclaiming "It's salt"

Christopher Reeve Superman. How come he's fast enough to go back in time, but not fast enough to save Lois in the first place?

Scene needed is Jor-El explaining that Clark is as strong as he believes himself to be. He can literally focus the entire power of the Sun if he's strong enough.

Pirates of the Caribbean it was pointed out Bootstap was strapped to a cannon and dropped into the sea but the logical conclusion that by lifting the curse Will had to kill his own father was never a plot point. not exactly a plot hole just a missed opportunity.

"Oh man, look how far down the track the T-Rex pushed our car!"

...and it was all a dream.

How did Inigo know the Man in Black was in love with Buttercup? It's an easy one to fix, because there are several points where Grandpa skips parts of the story, but it could have been a single throwaway line.

"The red fabric attracts phaser fire and other dangers"

There's a YouTube series called "how it should have ended" and 90% of them are basically answers to this question lol

In Frozen 2, the elemental spirits have trapped a kingdom in a magical barrier for many years as punishment for building a dam to stop a river. The day is "saved" by an earth spirit incidentally destroying the dam and freeing the river. There was this whole thing about the spirits calling out to Elsa to come and save them, but apparently the spirits had the ability the whole time to break the dam. The whole plot was basically pointless. Maybe instead they needed Elsa to break the dam, or needed to combine their powers.

“We’ve almost got some of their telecommunications cracked; the front end even runs on a laptop!” The Mac that sunk a thousand ships could have been merely clunky product placement, not a bafflingly stupid tech-on-film moment.

It was explained in a deleted scene. In Independence Day, our computers are based on reverse engineering their crashed ship. That and why would a hivemind alien race ever even need cyber security? Up to that point, they probably never encountered a scenario where a planet they were harvesting had an intelligent race on it, said intelligent race recovered a crashed ship of theirs, and said race was advanced enough reverse engineer it.

even if it demanded Simone Biles levels of mental gymnastics to save Carrie Fisher's most emotionally resonant moment from ROTJ

I don't think it's "gymnastics" to imagine that an orphan toddler might end up with some false memories of what she imagines her mother was like.

What I'd rather have had as a tiny change to "improve" the situation would be to confirm that Palpatine used some kind of Dark Side alchemy to drain Padme's life to keep Vader alive, I really like that notion. Wouldn't need to be with dialogue, even, just have some kind of scene showing Palpatine meditating and channeling something.

Then back to the Future part 2, Marty McFly should have arrived in the future where he disappeared 30 years ago and his children were never born.

Even if he did arrive history should have begun reverting itself, as his disappearance from the past should have altered the present until he returns.

As long as he experienced no ghosting effects, that would have meant that he was functionally immortal until he returned back to the present.

That entire scenario could have been avoided if doc Brown had said we've got a few hours until the universe begins to rectify the fact that you are not in the past with the temporal causality of the present future

I saw some criticism of Netflix's 'Ripley' adaption, based on the fact that Andrew Scott is in his late 40s, so his character (and all associated characters) had to be maybe in their late 30s but not much younger. They said that a father wouldn't be as interested in him returning the USA in the same way that he would be if his son was in his early 20s (as in the 'Talented Mr. Ripley' film). I thought they could just add a line from the father, saying he'd tolerated his son galivanting around Europe until now, but now needed him home because his father was starting to consider retirement and wanted him to take over the business.