I've never been able to find Michael Caine 'believable' as an actor.
As analogy, I can watch Only Foools and Horses and David Jason 'becomes' Del Boy for me. I can watch A Touch of Frost straight afterward and then David Jason 'is' DI Frost. If the next programme is The Darling Buds of May, I will then see Pop Larkin on my screen, rather than David Jason.
However it doesn't matter whether I'm watching Zulu, The Italian Job, Alfie, Funeral in Berlin or any other Michael Caine movie, all I ever see is Michael Caine on the screen, rather than the character that he's meant to be playing.
This might be of interest to his fans though:
https://www.rte.ie/entertainment/2023/0314/1362130-coin-mosaic-marks-90th-birthday-of-michael-caine/