Thanks for your question. Although WordPress supports PHP 8.0, plugins and themes may not support it, so upgrading our WordPress assets could affect many of our users. Our engineering team is aware of this and will update the PHP version available with WordPress as soon as it is safer to use it, but I'm afraid we can't provide you with an estimation on this.
You can periodically check our changelog to check if PHP 8.0 is available at https://bitnami.com/stack/wordpress/changelog.txt
Note we are currently using PHP 7.4.13, belonging to the 7.4 PHP branch, which will be under active development until November 2021 (plus receiving security updates until 2022), so using latest PHP 7.4 is safe. You can get more information about this in the link below
You can also check the official WordPress statement regarding PHP 8.0 at https://make.wordpress.org/core/2020/11/23/wordpress-and-php-8-0/