As a newbie I tried the new 20.5 mpm solver. Like you see the "jelly" effect is a splash with my file I followed the video but I missed something somewhere (at 14.50 on the youtube link below) I join my file, if someone could tell me where I made a mistake? :S
I tried to increase the stiffness like you told me, but a splash again... And yes, in the rubber toy flip there is certainly something that I don't know. I joined mine so you can have a look on the file or with the screen capture below...
Don't stress over that subnet with FLIP in it. Remove it completely if you like.
Your display flag is not even on the MPM solver, which means you're not looking at MPM solver's simulation result at all. You're looking at the FLIP simulation, which doesn't matter at all if your intention is to test MPM solver.
To me the MPM simulation works very similar to what the keynote showed. Jello like, no splash.