After the recent update and initial working out how, I've managed to create a folder (I've called it "andFTP") in my internal storage root, by clicking "External", and creating a new folder. I can upload and download files there just fine. Note my device doesn't have external/sdcard storage. However...

Having seen another post about ed25519 support, I've found the following. With a 2048bit RSA key, and settings->advanced->expert->SSH Provider=default I get the failure / error reported above. If I change settings->advanced->expert->SSH Provider="Secure (includes ED25519)" then the login is successf...