Minor nit: Kotlin is decidedly not a functional language.
Design patterns in OOP exist purely to solve the problems created by OOP itself. If you have a language with proper ADTs and higher order functions, the need for traditional design patterns disappear since the problems they solve are first-class features baked into the language.
The first-class replacement for the Strategy pattern (and many other patterns such as the Visitor pattern) is sum types (called enums in Rust).