What is your favourite thing to do in the Sims 4?

Coming here, reading posts of interest, and contributing - whether in general or helping some poor soul with a problem. If you mean actually in the game, then taking sims into the jungle to explore, become archaeologists, and be in tight with the locals. Another route is by having what amounts to a small farm. A sim can make a decent living selling produce, flowers and the like. If you get dragon fruit (takes time and patience but they are there, also on the gallery), you are really in clover with those.