Answer 1

Yes, Java virtual machine is platform dependent. JVM needs to be installed on your machine depending on what platform do you have (like Windows, Linux, Mac operating systems). JVMs are written differently according to the OS configurations. JVM executes Bytecodes (.class files) only which makes Java programs platform independent.
You can see more about JVM here : https://www.geeksforgeeks.org/jvm-works-jvm-architecture/