Using an "if" condition on "for" tag in "themes/custom/tribute/templates/layout/book-export-html.html.twig" at line 37 and 41 is deprecated since Twig 2.10.0, use a "filter" filter or an "if" condition inside the "for" body instead (if your condition depends on a variable updated inside the loop). See https://drupal.org/node/3071078.
Using an "if" condition on "for" tag in "themes/custom/tribute/templates/layout/book-export-html.html.twig" at line 37 and 41 is deprecated since Twig 2.10.0, use a "filter" filter or an "if" condition inside the "for" body instead (if your condition depends on a variable updated inside the loop). See https://drupal.org/node/3071078.