It's important to note that Chekhov's Gun was not originally about foreshadowing, but a piece of advice to playwrights about how every element in a play should have narrative relevance. The corollary to Chekhov's Gun is that if a gun mounted on the wall in act 1 is never used at all in the entirety of the play, then it should be omitted from the play entirely.
Corollary to the corollary: this does not suggest that the only way a gun (or other prop or bit of set dressing) should be allowed to exist is if it sees active use. In the classic example of the gun, it can never be used but still be relevant. A character who keeps a gun mounted above his desk in between hunting trophies is characterized by the presence of the gun, just like a character who leaves a gun on her nightstand next to a glass of water and a crucifix. A gun as part of a huge display of weapons that takes up an entire wall can tell us a lot without ever being used, too: is it a flintlock among muskets and swords or a desert eagle next to grenade launchers and tank shells?
And that's just the ways a script might specifically call out the presence of the gun. They're all relevant without seeing use, because their presence tells you something about characters and the space.
You could equally have the gun there as an incidental part of the set dressing, not called for by the script but perfectly logical. The script tells us that the space is cluttered with a wide array of objects that seems like it should be cleaned before someone gets hurt? A gun on a table would certainly help to paint that picture. The action takes place in a cabin in the country? A rifle leaning on the wall by the door might make the scene look more remote or lend verisimilitude to a character talking about fresh venison. A character is a soldier returning from the front lines? Well, a gun would complete the look without being mentioned or used in the script.
And, a gun can be not used in a way that is just as meaningful and relevant. A character comes in at the start of the play and puts a gun up on a shelf. When difficulties come, she looks at the gun, but never touches it. A grizzled cop's gun is always visible, but never used, with negotiation and de-escalation saving the day instead of violence. A character talks seriously about suicide and casts longing glances at a gun, but it's gone in the final scene and they're still there.
