How does the Remarkable store notes? Do you need to use their cloud service or can I use it as an offline notes/sketchpad then access the files via USB? And can

How does the Remarkable store notes? Do you need to use their cloud service or can I use it as an offline notes/sketchpad then access the files via USB? And can I load ebooks directly via USB? I’m happy to use the cloud service in general but I also am regularly in areas with absolutely no internet access and love that I can load ebooks directly onto my kindle via USB and that Highlights/notes in Kindle are a standard .txt file. I also want to be able to back up all my notes to my PC and access them there for safe keeping. That’s the only thing holding me from buying a remarkable, a fear of lock-in.