Almost certainly this problem is the result of an attack on your site: block_rce presumably indicates this a Remote Code Exploit (RCE).
Firstly delete the folder rce in /var/www/html/blocks, or move it somewhere safe so you can inspect it later. Your site may start working after this.
We don't know whether the attacker used the RCE to damage or alter your site, extracted data from the site, or just used it to determine if the site was vulnerable. Analysis of the server's logs and the rce folder may help establish this.
The best course of action would be to set up a new server and restore your site from a backup from before this problem started, presumably before 2021-05-27 02:27 based on your screenshot. This is a lot of work but it's the only way to be certain that any changes the attacker may have made have been removed.
Then you should update your site to Moodle 3.9.7. There have been 17 security fixes since Moodle 3.9.3.
If you have any internal procedures for handling security issues you should follow these too.