URL structure

You can remove the portal part. https://github.com/WPManageNinja/fluent-community-docs/blob/master/code-snippets.md#modify-portal-url-slug

Fixed =

<?php
if (!defined('ABSPATH')) {
exit;
}

/**

• Greek -> Latin slugify for FluentCommunity feeds
  */
  function pn_fc_greek_slugify($text) {
  $text = trim((string) $text);

  if ($text === '') {
  return '';
  }

  $map = array(
  'Α'=>'a','Ά'=>'a','Β'=>'v','Γ'=>'g','Δ'=>'d','Ε'=>'e','Έ'=>'e','Ζ'=>'z',
  'Η'=>'i','Ή'=>'i','Θ'=>'th','Ι'=>'i','Ί'=>'i','Ϊ'=>'i','Κ'=>'k','Λ'=>'l',
  'Μ'=>'m','Ν'=>'n','Ξ'=>'x','Ο'=>'o','Ό'=>'o','Π'=>'p','Ρ'=>'r','Σ'=>'s',
  'Τ'=>'t','Υ'=>'y','Ύ'=>'y','Ϋ'=>'y','Φ'=>'f','Χ'=>'ch','Ψ'=>'ps','Ω'=>'o','Ώ'=>'o',

   'α'=>'a','ά'=>'a','β'=>'v','γ'=>'g','δ'=>'d','ε'=>'e','έ'=>'e','ζ'=>'z',
   'η'=>'i','ή'=>'i','θ'=>'th','ι'=>'i','ί'=>'i','ϊ'=>'i','ΐ'=>'i','κ'=>'k',
   'λ'=>'l','μ'=>'m','ν'=>'n','ξ'=>'x','ο'=>'o','ό'=>'o','π'=>'p','ρ'=>'r',
   'σ'=>'s','ς'=>'s','τ'=>'t','υ'=>'y','ύ'=>'y','ϋ'=>'y','ΰ'=>'y','φ'=>'f',
   'χ'=>'ch','ψ'=>'ps','ω'=>'o','ώ'=>'o',

  );

  $text = strtr($text, $map);

  // Ενώνει συντομογραφίες τύπου Ε.Ο.Π.Υ.Υ.
  $text = preg_replace('/(?<=\b[a-zA-Z]).(?=[a-zA-Z]\b)/', '', $text);
  $text = str_replace('.', ' ', $text);

  $text = strtolower($text);
  $text = pregreplace('/[^a-z0-9\s-]+/', ' ', $text);
  $text = pregreplace('/[\s-]+/', '-', $text);
  $text = trim($text, '-');

  return $text;
  }

/**

• Attach custom creating hook after FluentCommunity loads
  */
  add_action('plugins_loaded', function () {
  if (!class_exists('\FluentCommunity\App\Models\Feed')) {
  return;
  }

  \FluentCommunity\App\Models\Feed::creating(function ($model) {
  $source = '';

   if (!empty($model->title)) {
       $source = $model->title;
   } elseif (!empty($model->message)) {
       $source = wp_strip_all_tags($model->message);
   }
  
   $custom_slug = pn_fc_greek_slugify($source);
  
   if ($custom_slug === '') {
       return;
   }
  
   $base_slug = $custom_slug;
   $slug = $base_slug;
   $count = 1;
  
   while (\FluentCommunity\App\Models\Feed::where('slug', $slug)->exists()) {
       $slug = $base_slug . '-' . $count;
       $count++;
   }
  
   // overwrite the plugin fallback slug
   $model->slug = $slug;

  });
  }, 20);

------ Try this one..