Have followed the trends and I now know Ember, Angular(both legacy and new), Vue(with and without typescript), and React(both classes and hooks). I've also used Svelte, and Stencil JS in my personal projects. In addition, I've also dived headfirst into GraphQL and Typescript pretty heavily lately.

Do I regret investing time in learning any of those frameworks or technologies?

Not at all. It was fun and interesting at the time I learned something different from each of them. Perhaps the most valuable thing I learned was that it is worthwhile to evaluate new technologies and to continue learning new things.

Does it devalue me as an Engineer to learn many things as opposed to becoming an expert in a single tech stack?

Much the opposite. A lot of the underlying principles and architecture remain the same and yet, I find each framework offers something new. Whether it's questioning some convention, or approaching a problem with a different paradigm, or just being heavily opinionated, I feel like I gained some value from each of these and had fun while doing so.