an Error 500, although technically server side, is caused by the PHP code on your site. So it is highly unlikely that there’s a problem server side causing the issue (that would more likely cause 503 or similar timeout or unreachable errors)
Out of interest, when was it last working? Because the PHP version was updated to PHP 8.3 in April 2025. so if it was before that, its possible your Joomla install is running an outdated php version that isn’t compatible with 8.3
Actually, looking at it, the current version of Joomla on the script installer is 6.0.1… so that might actually be part of the problem. You might want to try taking a backup of your site (How to backup your website), installing the most recent version of Joomla, and then if needed restoring your settings\database from the backup (I believe Joomla can be updated in place, but I’d never risk it myself)