Ideally you'd learn both, but I understand your time is limited. Choose based on whether you'd prefer to work on back-end stuff or front-end stuff.
Kotlin seems to be popular on the JVM for more greenfield work. However a lot of backend stuff seems to be Typescript/Javascript on NodeJS with Go close behind.
For job purposes I'd learn Typescript followed by Go. I'm not a fan of Typescript for the backend so this is based purely on getting a job.
Rust would be my heart not head language to learn. Realistically it has another 5-10 years to go before it's picked up for mass usage in industry, if it's picked up as Go is. It's a bit harder to learn and that's why Javascript/Python/Go are popular, a lot of people can use them in a few hours without to much learning.
Could be. But what are the numbers? There are 3,027 results for 'java developer' on Indeed, and 196 for 'kotlin developer'. (Obviously you have to take those particular numbers with a grain of salt - e.g. job listings that match Java frequently say something like, "Knows a language like Java or C++" whereas a job listings that match Kotlin are probably? looking specifically for a Kotlin dev.)
If you don't mind, what's your opinion on Java Vs scala? I keep hearing anecdotally that scala is better but without any concrete reasons.
Another benefit of Java: it's similar to C#, so most any company hiring for a C# dev would be open to hiring a Java dev. Learning Java simply opens more job opportunities.