Backend

there is no such thing as "best" languag. All of them have pros and cons, I personally prefer JS (Node + Express).

Java or Python🤔

Java can also be used as a back end, but it isn't encouraged. Rather, it's used for web applications. https://softwareengineering.stackexchange.com/questions/102090/why-isnt-java-used-for-modern-web-application-development

Whatever you find easy. It may be either PHP, or JavaScript or ASP.NET or Python or something else, but it varies among people.

how about java?

Python is a great choice.

from the point of security among java and JavaScript which is better?

https://www.sololearn.com/discuss/1112051/?ref=app

Hii