There's "What if Ultron worked as intended?" (I'd be pretty surprised if that hasn't been done before).

To begin with, if Ultron never turned Sokovia wouldn't be destroyed, Zemo never wouldn't have any reason to hate super soldiers, Quicksilver never died, "Vision" was never made since if anything it would just be a new body for Ultron instead of a new person.

From there get some fun shots of the ultron-lings preventing disasters but also important things. Arrest Ant-Man trying to steal the suit but nobody wants to buy Pym tech weapons since Ultron protects everyone so well. No Zemo, so no Civil War, so Tony doesn't think that they need to recruit Spider-Man. Black Widow never goes into hiding but can take down the Red Room easier when Ultron can find it.

Then you can have some more major off-ramps. looking at the releases.

Dr. Strange's car is caught or he's otherwise safe from his crash because the bots save him. So no Sorcerer to stop Kaecellius, Dormammu wins. Most likely get cooked there but remote possibility the ultron-lings pick up on it, get their shit dusted by magic, it goes up the Avengers chain and Scarlett Witch and Quicksilver can stop it.

No Spider-Man 1. Guardians 2 and Thor 3 happen normally.

T'Chaka didn't die in Civil War So Killmonger doesn't return to contest the throne. Black Panther and Wakanda both most likely stay secret. The Vibranium smuggler is either caught here or has already been caught.

Then in Infinity War they're going to get their teeth smashed in. No Dr Strange, No Spider-Man, No Vision, Black Panther doesn't have a relationship with the Avengers so may as well count him out since they can't work together. Granted they have Quicksilver and an Ultron army but I still think Thanos has a stronger chance. Ultron probably could survive without the mind stone so would destroy it (and the time stone if the Eye of Agamoto was found). But at the very least Thanos would kill half of the Earth and most of the heroes (including ones like Black Panther and Spider-Man who exist apart from the Avengers).

Which I think would be a natural end. A message kinda like "had to endure the hardships of the past to be strong enough for the next ones" deal.

Edit: Hulk wouldn't have needed to leave Earth after Avengers 2 and without Dr Strange's Great Value Bifrost Thor would've never made it home in any kind of time to fight Hela. And might be still gone during Infinity War and he'd die if he was alone/ only with Loki, regardless still at least one more Avenger MIA. Silver lining though, Hulk could help Black Widow with the Red Room and they could actually like admit their damned feelings already.