IIRC, the rM port currently has a bogus fallback Home set, that probably doesn't help.
Also, I have no idea *where* the stuff you're trying to read comes from in the first place, but it's also likely to just be stored in a place you're simply not currently looking at.
It's a file manager, you just have to point it at the right place

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And, no, there's no USBMS support at all on that platform either (at least not from within KOReader).
You'll probably have better luck getting answers from actual people with a rM by asking about that wherever it is they discuss these things (reddit? discord?). Because, as you might have noticed, there's no rM forum on MR

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