There can be a multitude of reasons as to why you are seeing 500 code errors
As suggested in the comment, you need to increase the log verbosity to get more details about the error
Based on your nginx configuration, the error file can be /var/log/nginx/error.log
or a different one.
Alternatively you can check the logs using journalctl
depending on the service management system in place
It could potentially be a permission denied
issue when accessing the static files so you need to make sure the user spawning the nginx processes has the correct access level
Please share the nginx configuration file and the permissions associated to the files to be served