Paul McCartney is one of the best songwriters and performers ever.
He has shown multiple times his ability to spontaneously write a song on topic given to him by someone else.
Here is a classic example.

https://youtube.com/shorts/CRsa5FAaec8? … aliWJf64f9

a more famous episode would be this.....

Paul McCartney Details The Time Dustin Hoffman Dared Him To Write A Song
By Hugh McIntyre,

Paul McCartney is one of the most successful and celebrated songwriters of all time. He seemingly has no issue penning a tune at any time, about anything. The superstar put his talent to the test years ago on a dare from one of Hollywood’s elite, according to the musician himself.

In the latest episode of the former Beatles’ podcast Paul McCartney: A Life in Lyrics, which sees him diving into the backstories behind some of his biggest hits and favorite tunes, the powerhouse musician shared a very fun story behind one of his own tracks. He revealed that his tune “Picasso’s Last Words” was written entirely based on a dare from none other than Dustin Hoffman.

The two men were reportedly together at some event when the challenge was posed by the actor. “Dustin Hoffman said to me, ‘Can you write a song about anything?’,” McCartney explained in his podcast. He answered without boasting, saying, simply, “Well, I don't know, Maybe.”

According to McCartney, Hoffman then said, “‘Just a minute.’ And he ran upstairs.” The Oscar-winning actor then “Came back down with a newspaper article about the death of Picasso,” who had passed away recently.

“He said, ‘See what Picasso's last words were. His last words to his friends were, ‘Drink to me. Drink to my health. You know I can't drink anymore’,” Hoffman then reportedly asked if McCartney thought he could write a song about that. The musician seemed up to the task.

McCartney explained that he “did happen to have my guitar with me, so I hit a chord and started singing a melody to those words.” Upon hearing what the Beatle came up with on the spot, Hoffman “was flabbergasted,” according to the music legend. Others who were at this get together must have felt the same awe, watching a master do something few, if any artists could manage.

“Picasso’s Last Words”—officially titled “Picasso's Last Words (Drink to Me)”—was released in 1973 by McCartney and his band Wings. The tune was featured on their classic album Band on the Run, which remains one of McCartney’s most beloved solo projects. While it was never spun off as a single, the cut remains an amazing demonstration of the singer-songwriter’s abilities–and apparently his willingness to accept a dare.