A lot more emphasis on functional programming & nicer syntax around it, preference of value types over reference types and immutability by default/opt in mutability, nicer parsing with Codable, nice pattern matching and destructuring syntax, native binaries by default, more flexible memory management.
Modern C# has both destructuring and pattern matching in switchs.
The memory model of swift seems obscolete, reference counting does not catch reference cycles and swift isn't faster than C#
C# isn't really missing features vs swift but it might have a less modern syntax