Having the same issue as this post, I decided to try to create my own keybindings within Jupyter vscode in order to replicate the behavior of the old Jupyter interface, regarding the effect of downarrow:

1. When the cursor is not at the bottom of a cell, move the cursor down
2. When the cursor is at the bottom of a cell, but not at the end of the line, move cursor to the end of the line
3. When the cursor is at the bottom of a cell and at the end of the line, move to the next cell

In order to do this, however, I need to use a "when clause context" to detect when the cursor is at the end of a line. I can't seem to find such a context key. (There is, however, notebookCursorEditorAtBoundary == 'bottom', which I believe detects if the cursor is at the bottom of a cell.)