It's because your .htaccess contains php_value statements, which we don't allow (users are not permitted to change PHP settings, especially the memory limit or execution time limits).
Invalid command 'php_value', perhaps misspelled or defined by a module not included in the server configuration, referer: https://allpeptides.net/
I just commented it out for you and the 500 error went away. Now it looks like you need to reinstall WP as the software itself is also broken.