So recently, I rewatched the Doctor Strange movie.
And since then, I am wondering where were the Avengers (or any other superheroes in MCU) during the events of the Doctor Strange movie?
Consider how little of the major events actually take place where the general public would be able to see them.
The initial fight takes place entirely within the Mirror Dimension so the only part anyone that isn't a wizard might notice would be the Ancient One appearing out of nowhere on the street.
The first battle for the New York Sanctum that we do see takes place entirely behind closed doors and the next is again in the Mirror Dimension so once again the only oddity the muggles would notice is the Ancient One appearing out of nowhere a second time albeit this time with a hell of a faceplant.
The final battle in Hong Kong was far more dramatic and destructive and would most certainly have drawn the eye of the Avengers but for the simple fact that from the perspective of anyone that isn't Strange, Wong and Mordo it never happened at all thanks to the Time Stone rewinding the entire thing.
In a nutshell to anyone that isn't one of the various wizards involved or Christine the only events out of the ordinary are an oddly dressed bald lady appearing out of nowhere in London and falling out of the sky in New York and neither was enough to draw the attention of the Avengers.
Wong: While heroes like the Avengers protect the world from physical dangers, we sorcerers safeguard it against more mystical threats.
Doctor Strange
The Avengers weren’t involved in the events of Doctor Strange because it is not the type of threat they deal with or even know about.
That said Doctor Strange takes place in 2016 to 20171. So during this time we know that the events of Avengers: Age of Ultron and Captain America: Civil War have already happened and it is before Thor: Ragnarok. This means that half of the Avengers are in hiding and on the run with Scott and Clint on house arrest. We also know that Thor is off world having left to find out who is pulling the strings with the Infinity Stones and as we find out in Thor: Ragnarok he is also bringing peace back to the Nine Realms. Banner is MIA after leaving in the Quinjet as Hulk and as we find out in Ragnarok he somehow made it to Sakaar.
Of the Avengers from Tony's side, Rhodey is paralysed and so presumably house bound. Peter is back home being the friendly neighbourhood Spider-Man with Tony looking out for him. Note though that these Avengers are all under the Sokovia Accords following Age of Ultron and so can't really act without permission.
Lastly, of course we have the Guardians and we know where they were: hanging out in the Andromeda galaxy, finding and killing dads and saving people for that cheddar cheese.
1 In Avengers: Endgame when Smart Hulk goes to the Battle of New York in 2012 the Ancient One remarks he is "about five years too early" making it 2017 after the events of Doctor Strange.