the options i know are:

• unraid (costs moneybut is the simplest to setup and comes with a bunch of extra features, app store etc)
• btrfs (though raid5/6 aren’t considered ready for production use)
• mergerfs with snapraid (technically not real time but it’s the most flexible)

external usb drives

i don’t like the built in file browser. you can’t drag and drop, no dark mode and you can’t view properties.