colorcolumn

The 'colorcolumn' option is used to highlight a particular column or range of columns.

This is useful for highlighting the current line, or for highlighting the column after 'textwidth'.

The screen column can be an absolute number, or a number preceded with + or -, which is added to or subtracted from 'textwidth'.

set cc=80  " Highlight column 80 
set cc=+1  " Highlight column 'textwidth' + 1
set cc=+1,+2,+3 " Highlight 3 columns after 'textwidth' 

A helper function:

function Line(pos)
  pos = pos or ''
  if vim.api.nvim_get_option_value('colorcolumn', {scope = "local"}) == tostring(pos) then
    pos = '' -- When reusing the same value, unset the colorcolumn instead.
  end
  vim.api.nvim_set_option_value('colorcolumn', tostring(pos), {scope = "local"})
end
vim.cmd("command! -nargs=? Line lua Line(<args>)")
--                -nargs=? means 0 or 1 arguments are allowed

vim.cmd("command! Line80 lua Line(80)")

This function can be used to highlight a particular line, or to unset the highlight of the line.