Which programming language to learn next (as a competitive programer before college)?

So as the title says my programming experience mostly comes from competitive programming (though I did build a website and learned the basics HTML, Javascript and CSS).

So I've basically only ever used C++.

No before going to college I'm trying to learn a new language. As of now, I'm planning to become a product manager.

Now to my question:

Which programming language should I learn next If I'm mainly interested in the intersection of both backend AND the user experience (the UI) ? — haven't really decided if I want to build mobile apps, desktop apps or OS's… OR in which order would you recommend me to learn them?

For now I am considering the following:
– Rust and GO

– Kotlin and Swift