Sims freezing and UI not working + some infinite loading

I had something similar and I have 4 in the house.  It’s happened several times but I’m not sure what the exact fix was (it was waiting on an action from one the sims and, once completed, everyone started moving again)

The last time this happened, I had a sim sleeping while others were studying, eating, etc.  when everyone froze as you described, I told my sleeping sim to wake up and after if got out of bed, all the other sims started moving again.