I have an interesting protocol for this.

Moonlight rituals. The idea is, you get a bunch of people together, say 20-50, in the same place at the same time. Everyone opens an app, and it takes control of the screens and gives semi-random actions - like hold up your phone to the user to the left of you, get everyone in a circle with phone screens on your chest and walk forward, enter the middle of the circle and slowly spin around, hold it up to take a picture of the moon...

The idea is, you constantly change the screen, take synchronized pictures, record audio, get flickers in gps signals, record fluctuations in the magnomiter.

The idea is to synchronize everything with millisecond precision, randomly take snapshots both across the group and between groups, and use all this to corroborate the fact that there was one user per phone present at this point in space and time. By using reality to generate enormously complex data sets, you can make it arbitrarily difficult to simulate, and doing it in real time could use cheap hardware and require processing orders of magnitude faster to spoof.

Doesn't matter how much processing you throw at it - a system like this would theoretically be able to measure gravity waves and stellar radiation - no way you to measure that and adjust your data before you time out the recording window

On top of nodes doing all this, you'd build a web of trust with random nodes spot-checking each other.

It's crazy and impractical, but I love the idea just because it's turning technology to magic - making group rituals to authenticate is just such a fun concept to me