Undefined constant

Hi, I updated to the latest optimiser version 0.8.0 from 0.4.5, and I got the following error:

Fatal error: Uncaught Error: Undefined constant "category_description" in /home/nusbizadclub/public_html/wp-content/themes/optimizer_pro_updated12_10_2021/framework/core-seo.php:26 Stack trace: #0 /home/nusbizadclub/public_html/wp-includes/template.php(772): require() #1 /home/nusbizadclub/public_html/wp-includes/template.php(716): load_template() #2 /home/nusbizadclub/public_html/wp-includes/general-template.php(204): locate_template() #3 /home/nusbizadclub/public_html/wp-content/themes/optimizer_pro_updated12_10_2021/header.php(27): get_template_part() #4 /home/nusbizadclub/public_html/wp-includes/template.php(770): require_once('/home/nusbizadc...') #5 /home/nusbizadclub/public_html/wp-includes/template.php(716): load_template() #6 /home/nusbizadclub/public_html/wp-includes/general-template.php(48): locate_template() #7 /home/nusbizadclub/public_html/wp-content/themes/optimizer_pro_updated12_10_2021/index.php(13): get_header() #8 /home/nusbizadclub/public_html/wp-includes/template-loader.php(106): include('/home/nusbizadc...') #9 /home/nusbizadclub/public_html/wp-blog-header.php(19): require_once('/home/nusbizadc...') #10 /home/nusbizadclub/public_html/index.php(17): require('/home/nusbizadc...') #11 {main} thrown in /home/nusbizadclub/public_html/wp-content/themes/optimizer_pro_updated12_10_2021/framework/core-seo.php on line 26
There has been a critical error on this website.

Please advise on what to do.
FYI: As of 20/10/2021
WordPress Version: 5.8.1
PHP version: 8.0
MySQL version: 5.6.51-cll-lve

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