WordPress is a free and open-source content management system written in PHP and paired with a MySQL or MariaDB database. Features include a plugin architecture...
A 500 error means the server could not process the request, but it does not identify the cause on its own. Note when it happened and check any error logs available for your website. The entries may point to an incompatible extension, a configuration issue or a resource limit.
If the error appeared after a change, investigate that change first. In WordPress, you can temporarily deactivate the suspected plugin. Before editing files, save a copy of them. When asking for technical help, provide the affected page address, the time and the relevant log entry, without passwords or other sensitive information.