Add below strings in diagnostic.lua.

  if last.message:find("unbound") or 
     last.message:find("is not accessed") or
     last.message:find("Cannot access member") or
     last.message:find("Argument of type") then
    return nil
  end

How to filter Neovim diagnostic (like below "randint" is ...) with some specific strings.

• Not kill all diagnostic function.
• Not suppress specific diagnostic level (like hiding less than warning level).

Add below text in neovim/runtime/lua/vim/diagnostic.lua, around line number 1065. Then, restart Neovim.

  for i = 1, #line_diags - 1 do
    table.insert(virt_texts, { prefix, virtual_text_highlight_map[line_diags[i].severity] })
  end
  local last = line_diags[#line_diags]

  -- ADDED FROM HERE
  if last.message:find("unbound") or 
     last.message:find("is not accessed") or
     last.message:find("Cannot access member") or
     last.message:find("Argument of type") or
     last.message:find("Import ") or
     last.message:find('Object of type "None"') or
     last.message:find('is not a known member of "None"') then
    return nil
  end
  -- UNTIL HERE

  -- TODO(tjdevries): Allow different servers to be shown first somehow?
  -- TODO(tjdevries): Display server name associated with these?
  if last.message then
    table.insert(virt_texts, {
      string.format('%s %s', prefix, last.message:gsub('\r', ''):gsub('\n', '  ')),
      virtual_text_highlight_map[last.severity],
    })

• If you add last.message:find("xxx") with or in above code, you can filter "xxx" also.
• If you're Mac user, find a location you installed Neovim. And modify Neovim/share/nvim/runtime/lua/vim/diagnostic.lua.
• If you're Linux user and installed with AppImage, modify /squashfs-root/usr/share/nvim/runtime/lua/vim/diagnostic.lua.
  • Then, type ln -sf /squashfs-root/usr/bin/nvim /usr/bin/nvim in bash/zsh.
• Be careful not to confuse with neovim/runtime/lua/vim/lsp/diagnostic.lua. You don't need to put /lsp/ before diagnostic.lua

If you modify local prefix = opts.prefix or '■' located at the above of previous code, you can change prefix of diagnostic also.

local prefix = opts.prefix or '👀'

• I'm not professional of Neovim nor lua. Change code with your responsiblity.
• As of today (3 Dec, 2022), I cannot find this info (= diagnostic filter) on the Internet (in spite of it seems this is normal demands). This code change may harm something?