There has been a critical error on your website

Getting an error message in the backend of the site which says, "There has been a critical error on your website. Please check your site admin email inbox for instructions". See attached screenshot with the error message.
Also, here is the error message notification/log we are receiving:

When seeking help with this issue, you may be asked for some of the following information:
WordPress version 5.3.2
Current theme: ColorWay Pro Responsive Theme (version 3.2.3)
Current plugin: (version )
PHP version 7.1.33



Error Details
=============
An error of type E_ERROR was caused in line 943 of the file /home/naturalb/public_html/wp-content/themes/colorwaytheme/functions/admin-interface.php. Error message: Uncaught Error: Call to undefined function ereg_replace() in /home/naturalb/public_html/wp-content/themes/colorwaytheme/functions/admin-interface.php:943
Stack trace:
#0 /home/naturalb/public_html/wp-content/themes/colorwaytheme/functions/admin-interface.php(125): optionsframework_machine(Array)
#1 /home/naturalb/public_html/wp-includes/class-wp-hook.php(288): optionsframework_options_page('')
#2 /home/naturalb/public_html/wp-includes/class-wp-hook.php(312): WP_Hook->apply_filters('', Array)
#3 /home/naturalb/public_html/wp-includes/plugin.php(478): WP_Hook->do_action(Array)
#4 /home/naturalb/public_html/wp-admin/admin.php(254): do_action('appearance_page...')
#5 /home/naturalb/public_html/wp-admin/themes.php(10): require_once('/home/naturalb/...')
#6 {main}
thrown

Tried loading from a backup but experienced the same issue with being unable to access the theme options in the backend of the site. I know this is definitely an issue with the theme based on the error message and not sure if I can get a fresh copy of the ColorWay Pro Responsive Theme or if getting a fresh copy of the theme would fix the issue.

What would be the best course of action to fix the error in the backend of the site without having to lose the current content in the site?