Orthogonally to my other answer, here's a version of SetVirtualEdit() that you can plug into your existing solution which does not require Python:

function! SetVirtualEdit() abort
  let saved_view = winsaveview()
  keepjumps normal! g0
  let is_on_leftmost_screen = col('.') == 1
  call winrestview(saved_view)

  if is_on_leftmost_screen
    set virtualedit=
  endif
endfunction

Orthogonally to my other answer, here's a version of SetVirtualEdit() that you can plug into your existing solution which does not require Python:

function! SetVirtualEdit() abort
  let saved_view = winsaveview()
  keepjumps normal! g0
  let is_on_leftmost_screen = col('.') == 1
  call winrestview(saved_view)

  if is_on_leftmost_screen
    set virtualedit=
  endif
endfunction

It works by moving the cursor to the left of the screen with the g0 command, and then checking if it's at the start of the buffer's line, using :keepjumps and winsaveview/winrestview to prevent the movement from affecting Vim's state.