Hi Matteo,

as I rememeber only by using Custom CSS.

To reduce Titles font size in blog view use those:

.wimble-article-classic-view .articles-leading .article .article-body .wimble-article-wrap .article-header h2,
.view-category .article-header h2 {
  font-weight: 600;
  font-size: 40px;
  line-height: 55px;
}


.wimble-article-classic-view .article .article-header h2 {
  font-weight: 800;
  font-size: 20px;
  line-height: 30px;
}

To reduce Title font size in single article view use that:

.view-article .article-details .wimble-article-details-title-wraper .wimble-article-details-title-wrap .article-header h1, 
.view-article .article-header h1 {
  font-weight: 800;
  font-size: 48px;
  line-height: 58px;}

J! Admin: Templates > Wimble > Template Options > Custom Code > Custom CSS

More tips inside Template Guide: https://www.joomshaper.com/documentation/joomla-templates/wimble/customization-tips