Why did Jimmy leave the Frank's room door slightly open?

In The Irishman (2019), Jimmy tells Frank a war philosophy:

Jimmy: In a war, you go from point A to point B. Sometimes, you spill a little beer along the way. That philosophy make sense to you?

Frank: Sure does.

And then Jimmy left Frank's room with the doors slightly open.

So why did Jimmy leave Frank's room door slightly open?

Best Answer

Collider analysed it pretty well:

The open door recalls an earlier scene in the movie where Frank is staying in Jimmy’s hotel room, and when Jimmy goes to bed he leaves the bedroom door open. It’s not an invitation—there’s nothing to suggest that Frank or Jimmy have romantic feelings towards each other—but it seems more psychological for Jimmy. The way the scene reads is that Jimmy, aware that he has plenty of enemies, is leaving the door open as means of self-defense. Literally and metaphorically, he doesn’t want the door shut on him. He doesn’t want to be boxed in and trapped by his enemies, but leaving the door open also gives him a vague sense of power. It’s an escape route of sorts. If you just leave the door open, you’re no longer trapped, although the sad irony of this scene is that in this moment Jimmy is trusting his protection to his future killer, Frank. robert-de-niro-the-irishman

For Frank to leave his own door open at the end is loaded with meaning. It’s a symbol of regret for killing Jimmy by mimicking his friend’s behavior, but it also speaks to the frailty of both men.