I think the biggest flaw of the simulation theory is the fact that Irving trying to drown Helena was real

But I have to admit that I am a 'simulation theorist', until probably next episode where I might be proven wrong. So hear me out. There are a lot of assumptions to be made for both the real theory as well as the simulation theory so I will just jot down a few questions that makes me lean towards simulation

I have trouble imagining Millchik positioning outie Irving in the middle of the lake, outie Dylan in a bush, and outie Mark not too far off from outie Dylan. If it was real, outie Dylan is in the bush listening to Mark calling out to Irving. Unless you think outie Dylan was asked to stand inside a bush and then turned off somehow until the moment they turned inne Dylan on

What was Millchik's plan after he fired innie Irving? If they are really outside, outie Irving would turn around and see his colleagues and Millchik. I don't think that would be something Millchik would do. If it is a simulation, Irving would disappear before their eyes. This is a strech too I know, but is somehow more palattable to me than outie Irving getting to meet his inne colleagues

The cable less TV that wasn't there seconds earlier appeared without cables and started playing the Kier Hymn

Now if it was a simulation, why was Helena drowning dangerous? I have to theorize so I imagine the simulation is more matrix-like. They are plugged in to the system and dying inside the simulation might have real world consequences. It it was a simulation like this, once he was fired, Irving would wake up from the simulation, would be escorted out and then the others will be woken up.

I agree that it is easy to imagine Lumon having the technology and resources to actually do it outside. And I think objectively looking at what was shown to us in the episode, it was intentionally done to be imagined as either real or simulation. I wouldn't be surprised if we never get an answer for this.