[crushthecurve]

If there was a mobile contact tracing app that used AGPS with accuracy down to ~1m maybe it would be useful?

Existing contact tracing apps use Bluetooth which can't be used to determine proximity with any reliability - solid objects (particularly human bodies) absorb significant signal.

Unless all protestors were holding their phones up high for unimpeded line-of-site connections then even protestors next to each other could 'appear' 20-30m away.

In most cases (especially in a protest situation) all Bluetooth-based contact tracing apps can tell you is that two devices are in Bluetooth range (so accuracy of ~30m?).