JVM can run on any platform that supports Java, as you’re building Kotlin directly into Java bytecode.
Multiplatform is for building native applications while using a single backend logic. You’ll have to write separate handlers for everything unique to the platform, according to documentation.
I’ve found that for single person purposes, a RAID array is unnecessary. I just buy beefy 8TB drives. If it dies, just download any recent torrents again or pull a backup