The site was crashing today with a fatal error.

It looks like it was this plugin with the latest .18 release:

[07-Dec-2023 19:39:54 UTC] PHP Deprecated:  Creation of dynamic property WC_Twoinc::$api_key is deprecated in /home/sitename/public_html/wp-content/plugins/tillit-payment-gateway/class/WC_Twoinc.php on line 46
[07-Dec-2023 19:39:54 UTC] PHP Deprecated:  Creation of dynamic property WC_Twoinc::$twoinc_search_host_no is deprecated in /home/sitename/public_html/wp-content/plugins/tillit-payment-gateway/class/WC_Twoinc.php on line 47
[07-Dec-2023 19:39:54 UTC] PHP Deprecated:  Creation of dynamic property WC_Twoinc::$twoinc_search_host_gb is deprecated in /home/sitename/public_html/wp-content/plugins/tillit-payment-gateway/class/WC_Twoinc.php on line 48
[07-Dec-2023 19:39:54 UTC] PHP Deprecated:  Creation of dynamic property WC_Twoinc::$twoinc_search_host_se is deprecated in /home/sitename/public_html/wp-content/plugins/tillit-payment-gateway/class/WC_Twoinc.php on line 49
[07-Dec-2023 19:39:54 UTC] PHP Deprecated:  Creation of dynamic property WC_Twoinc::$twoinc_checkout_host is deprecated in /home/sitename/public_html/wp-content/plugins/tillit-payment-gateway/class/WC_Twoinc.php on line 50
[07-Dec-2023 19:39:54 UTC] PHP Deprecated:  Creation of dynamic property WC_Twoinc::$plugin_version is deprecated in /home/sitename/public_html/wp-content/plugins/tillit-payment-gateway/class/WC_Twoinc.php on line 52
[07-Dec-2023 19:39:55 UTC] PHP Fatal error:  Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, non-static method WC_Twoinc::on_order_bulk_edit_notices() cannot be called statically in /home/sitename/public_html/wp-includes/class-wp-hook.php:324
Stack trace:
#0 /home/sitename/public_html/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters()
#1 /home/sitename/public_html/wp-includes/plugin.php(517): WP_Hook->do_action()
#2 /home/sitename/public_html/wp-admin/admin-header.php(303): do_action()
#3 /home/sitename/public_html/wp-admin/admin.php(239): require_once('/home/sitename...')
#4 {main}
  thrown in /home/sitename/public_html/wp-includes/class-wp-hook.php on line 324

A lot of plugins are throwing these deprecation errror in PHP 8.x but the fatal error at the end took out parts of the website.