It's practical to restrict yourself to a sound subset of Scala (the soundness issue they mention applies to a specific usage pattern that you can ban with a linter), and the issue is outright fixed in Scala 3.

The undecidability is real but you at least get what you're paying for - a certain amount of type-level programming is practical and useful in Scala. I'm not sure it's the right tradeoff but it's on (or at least close to) the Pareto frontier in a way that many languages aren't.