Kotlin: compatible with Java, JS, Wasm, Swift and even C++, ability to share code across all those platforms, way less verbose than Java, lots of useful functions in the standard library... I still don't understand why some people are saying it's just Java but worse

That is exactly why I switched to a custom rom (plus the fact that on top of these issues, I was stuck on an outdated version of the OS because my carrier wanted to include it's crappy apps no one ever used). Imo Xiaomi phones are very good on the hardware side, but the software is horrible to use when you're used to a near-AOSP OS.