Fix #4837 for those with older config

backend/lib/config.js

@@ -25,6 +25,12 @@ const configure = () => {
 
 		if (configData?.database) {
 			logger.info(`Using configuration from file: ${filename}`);
+
+			// Migrate those who have "mysql" engine to "mysql2"
+			if (configData.database.engine === "mysql") {
+				configData.database.engine = mysqlEngine;
+			}
+
 			instance = configData;
 			instance.keys = getKeys();
 			return;