When editing a scratch ("setloacl buftype=nofile") file, pynvim gives an error

I have the following vimscript functions:

fun! FilterClose(bufnr)
      wincmd p
      execute "bwipe" a:bufnr
      redraw
      echo "\r"
      return []
   endf

   fun! Finder(input, prompt) abort
     let l:prompt = a:prompt . '>'
     let l:filter = ""
     let l:undoseq = []
     botright 10new +setlocal\ buftype=nofile\ bufhidden=wipe\
       \ nobuflisted\ nonumber\ norelativenumber\ noswapfile\ nowrap\
       \ foldmethod=manual\ nofoldenable\ modifiable\ noreadonly
     let l:cur_buf = bufnr('%')
     if type(a:input) ==# v:t_string
       let l:input = systemlist(a:input)
       call setline(1, l:input)
     else " Assume List
       call setline(1, a:input)
     endif
     setlocal cursorline
     redraw
     echo l:prompt . " "
     while 1
       let l:error = 0 " Set to 1 when pattern is invalid
       try
         let ch = getchar()
       catch /^Vim:Interrupt$/  " CTRL-C
         return FilterClose(l:cur_buf)
       endtry
       if ch ==# "\<bs>" " Backspace
         let l:filter = l:filter[:-2]
         let l:undo = empty(l:undoseq) ? 0 : remove(l:undoseq, -1)
         if l:undo
           silent norm u
         endif
       elseif ch >=# 0x20 " Printable character
         let l:filter .= nr2char(ch)
         let l:seq_old = get(undotree(), 'seq_cur', 0)
         try " Ignore invalid regexps
           execute 'silent keepp g!:\m' . escape(l:filter, '~\[:') . ':norm "_dd'
         catch /^Vim\%((\a\+)\)\=:E/
           let l:error = 1
         endtry
         let l:seq_new = get(undotree(), 'seq_cur', 0)
         " seq_new != seq_old iff the buffer has changed
         call add(l:undoseq, l:seq_new != l:seq_old)
       elseif ch ==# 0x1B " Escape
         return FilterClose(l:cur_buf)
       elseif ch ==# 0x0D " Enter
         let l:result = empty(getline('.')) ? [] : [getline('.')]
         call FilterClose(l:cur_buf)
         return l:result
       elseif ch ==# 0x0C " CTRL-L (clear)
         call setline(1, type(a:input) ==# v:t_string ? l:input : a:input)
         let l:undoseq = []
         let l:filter = ""
         redraw
       elseif ch ==# 0x0B " CTRL-K
         norm k
       elseif ch ==# 0x0A " CTRL-J
         norm j
       endif
       redraw
       echo (l:error ? "[Invalid pattern] " : "").l:prompt l:filter
     endwhile
   endf

(see this website)

and this pynvim code:

dir = os.listdir(self.projectDir)
to_load = self.vim.eval(f'Finder({str(dir)}, "Enter the name of the project")')

When I run the code, I get this error:

neovim / pynvim

When editing a scratch ("setloacl buftype=nofile") file, pynvim gives an error #445