I have found Ghost and WordPress templates
but no template for opencart, how can I install it?
Unfortunately, we can’t provide templates for everything - but hopefully, the templates that exist for Ghost and Wordpress should give you enough of an idea of how to deploy Opencart on us.
A quick Google led me to this OpenCart Docker image https://hub.docker.com/r/bitnami/opencart/ which should work,
Here is the blueprint I did for OpenCart deploy on render, but failed to deploy