It is surprising that after all these years, there is still no good way to transfer files between two devices over USB. MTP exists but it was never widely supported and it seems like even the support it did have is slowly rotting as the answer became just connect everything to cloud storage.

reMarkable tablets end up exposing a USB ethernet device with a /23 private subnet and listing an IP address to visit in a browser. It works much more reliably than it should.