WordPress / Moodle website - fix errors, secure and cleanup

This client's WordPress site uses a Moodle bridge and it now throws a fatal error as soon as the homepage loads. One can no longer reach the Moodle area, and while digging through the server the client noticed unfamiliar files and folders that look like injected code. I need the site brought back to a stable, hack-free state and then hardened so this doesn’t happen again.

What I expect from you:
• Diagnose and resolve the fatal error that breaks the WordPress-Moodle integration: https://prnt.sc/7tcCjUh5ct4n
• Hunt down and remove every fragment of malicious or suspicious code on the server.
• Verify the integrity of core WordPress files as well as all plugins and themes, repairing or replacing anything altered.
• Update WordPress, the Moodle component, and all plugins without breaking existing functionality.
• Ensure plugin and theme compatibility after updates, testing critical user flows on both WordPress and Moodle pages.
• Apply security best practices (e.g., secure file permissions, strong .htaccess rules, malware scanning with tools such as Wordfence or Sucuri, login-hardening, backup routine).
• Provide a brief post-cleanup report summarising what was found, what was fixed, and recommendations for ongoing security.

The job is finished when the site loads error-free, passes a malware scan, and all Moodle and WordPress features work as expected.

Access data will be provided to the freelancer doing this job.