At least the lucky ones having Android 12 as baseline can now make use of Java 11 subset (because as usual Google only takes the parts of standard library they care about).
I’ve worked for 2 companies so far which maintain a bit of Android code and neither used Kotlin. GitHub search for “#android language:Java” reports 49K repositories, while “#android language:kotlin” reports 25K repositories. GitHub is biased towards greenfield projects, not legacy corporate codebases, so I’d expect the ratio of Java to Kotlin code in non-open-source software to be much higher. I wouldn’t be surprised if it’s more than 10 times higher.