Ah, now that could be a clever way of going about making a solid film - Napoleon on Elba, weary, defeated, jaded, reflective. He talks to someone about his career, his decisions, his achievements and regrets, Could be his mother or sister, who were both there at times, or an officer or some visiting 'tourist'. Have extended flashback scenes to 5 or 6 key moments, but always come back to the conversation, on how Napoleon perceives these events in hindsight, on the meaning of what he did, on the realities of lost glory and love and exile.
Finish the movie with him deciding to stake everything on one last bid for power and triumph, closing with a postscript of text noting the initial re-claiming of the throne, but then defeat at Waterloo, and eventual ending in a far worse exile on St Helena. Something like that could perhaps work. No attempt to tell his full life story, more a reflective piece with some main themes or threads that drive the narrative and are held up for examination over the course of the film.