Not the usual case for a regeneration story, Jodie Whittaker's final Doctor Who episode, "The Power of The Doctor" is the show's biggest multi-Doctor story ever. There are always two Doctors with every regeneration story as one turns into the other, but they aren't multi-Doctor stories as such, as the two actors are not on-screen at the same time. The only other time a proper regeneration story has been multi-Doctor was the previous regeneration episode, 'Twice Upon a Time', where Peter Capaldi shared the episode with the First Doctor, now played by David Bradley.
While there have been many multi-Doctor stories over the nearly 60 years of Doctor Who, most of the audience would never have guessed that the 13th Doctor's final episode would be the biggest of them all. The pandemic may have stopped writer Chris Chibnall from doing a proper, full-on multi-Doctor story, but for the episode celebrating 100 years of the BBC, he used that to his advantage. As the guardians of the edge, a place where all the Doctor's previous consciousnesses reside as the current regenerates into the next, the 13th Doctor comes face to face with past versions of themselves. This allows past Doctors to have a quick moment with the 13th Doctor without it feeling cheap or rushed. On top of that, with 5th Doctor Peter Davison and 7th Doctor Sylvester McCoy getting scenes with their respective companions Tegan and Ace, this allowed them to be in a scene proper, old costumes and all. And with David Tennant returning at the end of the episode, that means there are a total of eight Doctors in this story, making it the most amount of Doctors in a multi-Doctor story to date.
Why The Whittaker Era Hasn't Had A Proper Multi-Doctor Story
One of the main reasons why the Whittaker era hasn't had a proper multi-Doctor story is due to the pandemic and it making it harder for the team to bring in past Doctors properly. Also, multi-Doctor episodes are usually saved for some form of anniversary which they air a special episode for, and there hasn't been one during Whittaker's era (apart from the centenary special, of course). Had Whittaker and Chibnall stayed on another year for the Doctor Who 60th anniversary then the likelihood of a proper multi-Doctor story would have gone up.
Another reason is the introduction of Jo Martin's Fugitive Doctor. After first appearing in "Fugitive of the Judoon" in Doctor Who series 12, she has appeared alongside Jodie Whittaker's 13th Doctor a few times. These episodes could be classed as multi-Doctor stories, just not with an incarnation of the Doctor the audience was familiar with before.
Will Jodie Whittaker Ever Get A Proper Multi-Doctor Story?
If Doctor Who's past is anything to go by, Jodie Whittaker will get a proper multi-Doctor story at one point or another. David Tennant returned for the 50th anniversary, and now he's returning for the 60th as well. The 1st and 2nd Doctor William Hartnell and Patrick Troughton returned for the first ever multi-Doctor story "The Three Doctors" alongside the 3rd Doctor Jon Pertwee. With Whittaker already saying she would love to return to the role, it's only a matter of time before she returns for an anniversary special, opposite whoever has the keys to the TARDIS at the time.