I was going to suggest playing with toddlers if you want resistance from the game :D
Having autonomy on leaves me with plenty resistance from all my Sims. Especially in Sulani - no Sim is taking my directions there seriously and will drop it from their queue repeatedly.
I often struggle to making things work as they were intended, so I'm not really looking for ways to make it more challenging.
But, having said that, getting Mua Pel'am cleaned up completely and exploring the beach cave to restore the wall painting is something that takes time at least, offering a challenge of patience and consistent effort on the player's part. I like that this isn't just easily done overnight.
Sticking through the last levels of careers can also be challenging in terms of mustering patience. Is patience a boring challenge? For some, probably. But it is a life simulator in the cute category, so I'm not sure how much challenge it is meant to contain.
Achievements are more natural in other types of games.
There is an achievement list in Sims 4, @Wenzel - have you checked that and gotten everything on it?
