Up arrow goes up. Down arrow goes down. The notelist is displayed for each notebook as you move to it. Enter selects. Then the up and down arrows work in the note list for that selected notebook.
However, if you want to move the focus to the note / tag list (also known as the "side bar") use Ctrl + Shift + S. (See this similar post of yours where keyboard shortcuts are mentioned).
It does seem that Joplin will not accept mp3 files from the clipboard. However drag and drop as well as the "attach" tool do work. I do not know if the inability to paste an mp3 is intentional, or because Joplin cannot recognise it as a file type that should be attached, or Joplin should recognise it as such and it is a bug.
Again there has been little information provided to allow an attempt to answer this. However if you are trying to backup your OneDrive data and OneDrive is giving you the error is it not more of a problem with OneDrive?