Python is a little more readable, but both Python and Kotlin are perfectly clear in this case:
sorted((u for u in users
if u.last_name.startswith("S")),
key=lambda u: u.last_name
)[:3]
If last_name is a function, which it often would be in Python, it gets better:
sorted((u for u in users
if last_name(u).startswith("S")),
key=last_name
)[:3]
However, I think you probably got the sort key wrong if you're taking the first three items of the result. Maybe you meant key=abuse_score, reverse=True, or something.
