During a January 2021 LA Times interview with Emily Zemler, Stanley Tucci said that he was originally cast as Sam and Colin Firth as Tusker, but during their pre-filming discussions they both came to agree that they should switch the roles: "'We sat down and started talking about the script and where we'd be shooting, and then Colin said, "Stanley, I think maybe we should switch roles,"' remembers Tucci, who initially brought the film to Firth after meeting with Macqueen. 'I said, 'I've been thinking the same thing." And I don't know why. I just felt it. So we read both ways for Harry-and I could tell Harry was panicked when we told him-and it was evident.' 'It was an amazing process,' Macqueen adds. 'They brought that to me, and we decided to do an audition, which is an amazing privilege for a writer-director to have two people like Stanley and Colin sitting in a room reading both roles. I picked five or 10 scenes from the film, and they were kind of brilliant at both roles, as you can imagine. But there was just something about the quintessential Englishness that Colin brought to Sam and a kind gregarious energy that Stanley immediately brought to [the American] Tusker, which made the lighter moments in the film really sing. It just felt right all of a sudden.'"
When Stanley Tucci agreed to do the film, director Harry Macqueen asked him if he had any ideas as to who could play his partner. Ideally, he wanted someone that Tucci already knew well so the intimacy between them would be spontaneous. Tucci immediately suggested Colin Firth with whom he has been close friends for many years.
To get a better understanding of the disease of dementia, director Harry Macqueen volunteered a lot with dementia charities and briefly worked at a London hospital that specializes in the condition.
The idea for the film came when a friend of director Harry Macqueen had to place their father into a care facility as he had early onset dementia. Macqueen became fascinated by the disease and its emotional repercussions on those around the afflicted and spent the next 2 years researching the subject.
The film was mainly shot in the Lake District in Cumbria, UK.