The error message "Database server list can't be accessed: 500 GraphQL Internal Server Error" in Plesk indicates that there is an issue with the GraphQL API used to retrieve the list of database servers.

To address this issue, you can try the following steps:

1. Check Plesk Logs:

   • Review the Plesk error logs for any specific error messages related to the GraphQL API. The logs are typically located in /var/log/plesk.

2. Restart Plesk Services:

   • Restart Plesk and related services to ensure that any temporary issues or hung processes are resolved.
   bash

   sudo systemctl restart sw-cp-server sudo systemctl restart plesk

3. Check Database Server Status:

   • Verify that the database server (e.g., MySQL or MariaDB) is running and accessible from the Plesk server.

4. Check for Updates:

   • Ensure that Plesk and all installed extensions are up-to-date. An outdated or incompatible extension could potentially cause this issue.

5. Check for Custom Extensions or Modifications:

   • If you have custom extensions or have made modifications to Plesk, consider if any recent changes might be causing the GraphQL error.

6. Rebuild the GraphQL Schema:

   • You can try rebuilding the GraphQL schema, which might resolve any potential issues with the API.
   bash

   plesk sbin pleskext utility --do-node-action regenerate-schema

7. Check Disk Space:

   • Verify that there is sufficient disk space available on the server. Lack of space can sometimes lead to errors in Plesk.

8. Clear Browser Cache:

   • Clear your browser's cache and cookies. Sometimes, cached data can cause issues with the Plesk interface.

9. Check for Conflicting Software:

   • Verify that there are no conflicting software or services running on the server that might be interfering with Plesk's operation.

10. Contact Plesk Support:

    • If none of the above steps resolve the issue, consider reaching out to Plesk support for further assistance. They can provide specific guidance based on your server's configuration.

If the issue persists, it's recommended to gather detailed information about the error and contact Plesk support for further troubleshooting. They will be able to provide specific guidance based on the error logs and the configuration of your Plesk server.