WEBSITE_NODE_DEFAULT_VERSION is not working in Linux.
WEBSITE_NODE_DEFAULT_VERSION is Windows only property. Click here for more information.
Linux apps should use LinuxFxVersion setting.
How linuxFxVersion is added in an ARM template?
Linux apps should include a linuxFxVersion property under siteConfig. If you are just deploying code, the value for this is determined by your desired runtime stack in the format of runtime|runtimeVersion.
If you are deploying a custom container image, you must specify it with linuxFxVersion and include configuration that allows your image to be pulled, as in Web App for Containers. Also, set WEBSITES_ENABLE_APP_SERVICE_STORAGE to false, since your app content is provided in the container itself: