Display taxonomy term name or other fields without encoding (especially without encoded &'s)

The solution is using this kind of render array as a return value

Array
(
    [0] => Array
        (
            [#markup] => Drupal\Core\Render\Markup Object
                (
                    [string:protected] => anime & manga
                )

        )

)

Putting the value in #markup prevents HTML filtering, while having the Markup Object there prevents XSS filtering on the string. In code, use something like:

<?php
$elements[$delta] = ['#markup' => \Drupal\Core\Render\Markup::create($label)];

This was used in a field formatter but it can likely go in any preprocess hook too.