Minecraft 1.17 requires Java 16. PloxHost will automatically detect if you're running 1.17 or not and change your java version if needed.
If this fails to update, you may see an error such as:
Exception in thread "main" java.lang.UnsupportedClassVersionError
You can manually change your Java version to 16 in your ploxhost.yml file.
Please see: https://support.plox.host/en/knowledgebase/article/change-java-version