https://youtu.be/1p_8eSaUfJM?t=418 [youtu.be]
At 6:58 they demonstrate very fine collision detection for the feet.
What is the name of the effect? It looks 'physical', not like some vector math trickery with IK-effectors.

I dont think it demonstrates any collision detection, I believe the feet are transformed with the platform and FBIK computes how the body reacts

there are other examples in the launch video with the "collision" mostly the same principle of applying simple "collision" to certain joints like hands/fingers using Ray SOP or any other SOP based solution and then use them as targets for FBIK solve