Having chosen Racket and F# as my chosen “after work” languages, there is a common struggle. What I have done is choose books and then implement whatever they go through in Racket or F#. One excellent book is The Ray Tracer Challenge. It’s relatively language agnostic (I say relatively since it sort of assumes an imperative or OOP language), and my F# has really improved with it. I plan on also doing it in Racket. There’s a lot of books like that where the book is a sort of “from scratch” book, which makes it great to use your own language, even if they use another language in the book.