How to use read more text

Sure, this is possible. The starting point is a filter like this, which I understand you are currently using in some form:

add_filter ('excerpt_more','wpse333680_more_text',10,1);
function wpse333680_more_text ($more-text) {
  return 'Everything you always wanted to know about this >>';
  }

The function you use for the filter can easily be reused elsewhere. You could echo it anywhere in a theme or plugin (or even in a shortcode):

echo wpse333680_more_text();

If this is not enough you could modify the filter to include conditions so it reacts differently to various situations:

add_filter ('excerpt_more','wpse333680_more_text2',10,1);
function wpse333680_more_text2 ($more-text) {
  if (condition)
    return 'Everything you always wanted to know about this >>';
  else
    return $more-text . 'Everything you always wanted to know about this >>';
  }

Depending on the condition this would either replace the $more-text completely or concatenate the string to it.