Deathloop has an invasion mechanic that lets you plunder other players' worlds, ruining their run by picking them off. It's essentially Arkane's answer to Dark Souls, only it's not done through in-game items but menus. You have levels, gear, and challenges to complete as you alternate from Colt, the protagonist, to Julianna, the antagonist.
However, when you're playing Colt and you're on the cusp of finally killing all the targets, you probably don't want to lose that progress. For many, the idea of it all falling apart because another player snuck in with a handgun and a mean demeanor is terrifying. The anxiety and risk of that happening might be fun for some, but if that isn't you, fret not as multiplayer can be disabled.
There are three options when it comes to multiplayer invasions in Deathloop. You can set it to friends only, online, or singleplayer. During the tutorial and prologue, it defaults to offline, so you don't have to worry about it until the first encounter with Julianna after the lengthy introduction. After that, if you want to switch it off, here's a quick guide on how.
Go To The Planning Menu
Deathloop's planning phase is accessible in two ways. You can either exit your current location or navigate to the main menu. The latter will forgo all progress you've made in a zone, however, but it is quicker. Once you've done that, you should be brought to a hub with various different levels, your loadout, documents, clues, and so on.
In the top left, you'll see your name and profile next to the cog icon (settings). Simply left-click your profile banner and it will flick between the three modes. Under your name, it will say friends only, singleplayer, or online.
Click your name until it says singleplayer. Now, when you load into a level, nobody will be able to invade you bar the AI Julianna (she's much easier to take down than another player). Have fun breaking the loop without interruption. But hey, that doesn't mean you can't spoil other people's fun.