Backend Programming - where to go next after Java?

Short Form Question --> NodeJS/Javascript is not my cup of tea after spend 3+ months on them. All I know is core Java, what do you guys recommend to learn next to improve my skillset?

Long Form Question --> I have been doing core Java development for about 5 years (Interfacing with SQL DBs using JDBC, RMI, Thread programminpg etc) and wanted to update my skill set. So I started learning NodeJS/Javascript and even after spending 3+ months, still don't get that comfy feeling with it. It is probably the "flexibility/weirdness" of Functional Programming/Callbacks/Asynchronous stuff which is the core of NodeJS/Javascript or something else. Maybe I coded in core Java for too long with its clean/strict/structured approach that is very different from NodeJS/Javascript. Anycase, there are other programming languages that might suit my skillset - is Python a good option (or even Go?). I am looking for a popular/indemand programming language for next career move. Thanks!

PS: I am not saying one language is better or worse than other, just requesting some feedback to learn new programming languages that I don't have experience with.