> I've gone the other direction, which is basically "Typescript everywhere", or at least as much as possible, i.e. React on the front end, NodeJS on the backend, and Capacitor for apps (note Capacitor may not be appropriate for all types of apps but in our case it was).

Absolutely bad advice and totally disagree.

So having a language such as TypeScript which is already built on top of an even more immature language such as Javascript in critical systems software or highly regulated settings is a good idea?

Having it on the backend is also bad enough, but everywhere really an indication of not being able to adapt into using a properly designed language for the specific use-case and just being inflexible because you are 'used to the language'.

This is not even talking about the entire TS/JS ecosystem which is has a sea of libraries which most of them are also immature and not production-grade at all.