Immersion for me is when you cross NPCs engaged in something that has either no relation or no involuntary relation to the playable character.

I think of games like Elder Scrolls or Cyberpunk or Read Dead Redemption 1 & 2 where you can be walking somewhere and come across something in progress. Most immersive is when you can ignore the situation entirely if you choose to. Even more would be ignoring it and you never seeing it mentioned again in your playthrough. I’m not sure I can name any game that does this, in my experience. But I would love to play a game like that where I am on my way to something/somewhere and something interesting is happening and I have to make a choice to either experience this now before I never can ever again in this playthrough or keep going where I’m going. Kind of like real life and you see something crazy on the street going to work. If you don’t stop and look at that now, you will never see it again in your life unless it was recorded. You get a consequence of either missing out on work but seeing something crazy cool or the consequence of missing out on something crazy cool but making it on time for work.

I also find myself most immersed when the devs create a world that feels lived in and with things that don’t have official explanations. I think RDR1 & 2 have done this so well. I’m a player who likes to go off the beaten path and explore anything and everything. Coming across a random hatch in the middle of a grassy meadow but is never explained in game is so fascinating to me and I’ll spend many minutes trying to find any clues about what this is in the area. Very much like the real world and walking through an alley and finding a burned out car or something that just doesn’t get seen often but gets you wondering about the backstory and checking the nearby area for clues to see what may explain how this got here.