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

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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.