Strategic Writing for UX is a popular one. I started out by reading it and would recommend it.
What you're describing is called "microcopy."
Here's a really good book about it, highly recommended:
https://smile.amazon.com/Strategic-Writing-Engagement-Conversion-Retention/dp/1492049395/
Examples of style guides/design systems that cover this topic:
I never took any courses, but I did read the book Strategic Writing For UX, which was really helpful. That and Microcopy: The Complete Guide are both highly recommended in the UX writing community.
There's also a free UX Daily Writing Challenge that you can do on your own, which is a great way to build up your portfolio if you don't have any UX writing samples (or even if you do, it'll add more variety to the samples you have). You can also try designing the UX for each challenge to get familiar with design. In general, though, I don't think it's a deal-breaker for most companies if you don't know much about design.
This book changed the way my team works with microcopy.
https://www.amazon.com/dp/1492049395/ref=cm_sw_r_cp_apa_fabc_Np.VFb23ENV8P
I work on the design side so I don't know much about UX writing. Writing is actually my weakest skill which I'm trying to improve. I would google UX writing and UX writing jobs. There are a ton of resources online. Here's one I just found:
https://www.avoagency.com/articles/how-to-get-started-in-ux-writing
This is a book on my reading list to check out:
https://www.amazon.com/dp/1492049395/
On the side, I do recommend learning the basics and concepts of interactive design as well as some coding so you can speak the language when collaborating with designers and developers.