There has been a critical error on your website – won’t fix no matter what

So I’ve got the dreaded error too it seems. Apparently it’s a very common issue but I can’t really seem to get a hang on the fix.

One of the plugins my theme uses is causing the error as per the log I got in the email WordPress sent to my admin email. Here’s the full log

Here’s some additional information:
WordPress version 5.5
Current theme: Setech | Shared by WPTry.org (version 1.0.2)
Current plugin: RB Essentials (version 1.0.1)
PHP version 7.3.19

The website was running fine until yesterday on the exact same configuration. I made no changes that caused this error.

As you can guess, I have absolutely zero ideas what this means. I’ve tried disabling the plugin and reloading the site but it didn’t work. Also, if I try to change the theme I get an HTTP 500 Internal Server Error(File “/home/younited/domains/younitedsupport.com/public_html/wp-admin/themes.php” is writeable by group) when clicking on the themes pages in WordPress.

The same site on my localhost works just fine BTW. Everything is identical between the two sites. Any ideas on how to fix this?