For what it's worth, we had much better response from our kids with Gravitrax the Game (https://www.ravensburger.co.uk/en-GB/products/gravitrax/expe...) than the regular one. The material is basically the same (and thus could also work at extending a starter set), but there are cards with puzzle included, difficulty ramps up nicely, and the kids got more involved than with the "freeform" approach.

Turing Tumble has also been a big hit at our place, but it's clearly more for older kids (https://upperstory.com/turingtumble/)

UpperStory also has a new game (Spintronics) which looks awesome, but I haven't had the opportunity to test it.