Why in archive page doesn´t show read more button with excerpt?

You are using the wrong filter. Depending on how your theme is built, there may be two solutions.

1. If the theme uses the wp_trim_excerpt function, the
   excerpt_more filter inside that function will only be called if
   there is no excerpt passed to that function. At the end of that
   function there still is the wp_trim_excerpt filter that you could
   use to append anything to the result.

2. If the theme uses the get_the_excerpt function to echo
   the excerpt there is a filter with the same name that you may use.

Both solutions may work at the same time, so don’t overdo it.